Pakistan's army has begun a ground offensive in the volatile tribal region of South Waziristan. The army has been massing troops near the militants' stronghold for months. But what lies in wait for the army as it finally takes on the Taliban on their home terrain?
Where is Waziristan and what is it like?
Waziristan is a mountainous region in north-west Pakistan, bordering Afghanistan.
It is part of the Federally Administered Tribal Areas (Fata), a semi-autonomous region where the central government exercises limited control through a political agent.
For administrative purposes it is divided into two "agencies" - North Waziristan and South Waziristan.
Winters are harsh, making large tracts of the already inhospitable terrain almost inaccessible.
The tribal society found in North and South Waziristan is extremely socially conservative with a fierce reputation as "warriors".
North Waziristan is dominated by the Wazir tribe. This tribe also extends into South Waziristan and makes up one-third of its population. The remaining two-thirds of South Waziristan's population are Mehsuds.
Why is Waziristan a target?
South Waziristan and the surrounding region have been described by US officials as "the most dangerous place on earth".
Many analysts believe the area could harbour some of the world's most wanted men - including al-Qaeda leader Osama Bin Laden.
It was the home of former Taliban chief Baitullah Mehsud, who was killed in a suspected US drone strike in August 2009. It is also home to his successor, the current Pakistani Taliban leader, Hakimullah Mehsud.
North and South Waziristan form a lethal militant belt from where insurgents have launched attacks across north-west Pakistan as well as into parts of eastern Afghanistan.
South Waziristan is considered to be the first significant sanctuary for Islamic militants outside Afghanistan since 9/11. It also has numerous training camps for suicide bombers.
Pakistan's government is under considerable pressure from the US to tackle militancy there.
Analysts also say dislodging al-Qaeda-linked Uzbek and Arab militants in the area is an important goal.
What has happened so far?
The Pakistani army has maintained a brigade headquarters in the Wana region of South Waziristan since 2004.
But since May 2009 troops have been massing in large numbers in the semi-tribal areas on the periphery of Waziristan.
In the past few months the Pakistani army, working with local paramilitary forces such as the Frontier Corps, has launched some artillery and air strikes against Taliban militants.
SENIOR MILITANTS KILLED
2 October: Reports that Tahir Yuldashev, Uzbek militant chief was killed in August drone attack
29 September: Irfan Shamankhel, close to Taliban leader, killed in drone strike
28 September: Kalimullah Mehsud, Taliban leader's Hakimullah's brother, killed in clash in South Waziristan
15 September: Top militant Ilyas Kashmiri killed by missile in N Waziristan
6 August: Baitullah Mehsud, Taliban leader killed in suspected US drone strike in S Waziristan
But until now the army has said it wanted to surround the militants and use air power and artillery to ''soften them up".
This is in contrast to its recent campaign in the Swat valley where it suddenly began a three-month ground offensive in the summer of 2009 and largely succeeded in driving out Taliban fighters entrenched there.
People have been fleeing the Waziristan area for some months in anticipation of fighting.
The US has also been involved in attacks on militants in Waziristan, where suspected drone strikes have killed a number of senior Taliban militants in the region in recent months.
It was one such missile attack which killed Taliban chief Baitullah Mehsud at a family compound in South Waziristan.
What are the challenges of operating in South Waziristan?
The harsh mountainous terrain is often cited as a major challenge for the army. The gullies, ravines and high mountain trails make arduous going and provide many hiding places for militants.
Knowledge of the terrain is vital - and in this respect the militants have the advantage.
However, the BBC's M Ilyas Khan in Islamabad says that the terrain in the Swat valley, where the army took the battle to the Taliban, was more difficult than that found in South Waziristan because it is more densely forested.
The Malakand division which includes the Swat valley is also a larger area than that in which any Waziristan offensive is likely to take place.
Weather will play a role. Snow is likely to blanket parts of the region from early December - particularly the Makeen area which is a Mehsud stronghold.
This is likely to pose a problem for militants and troops alike. However, the cold has not prevented the army from launching operations in South Waziristan in the past.
What might be a deciding factor is the militarised psyche of society in Waziristan. The Wazir and Mehsud tribes are often described by analysts as "born soldiers" willing to fight to the death.
PAKISTAN ARMY HAS A FULL RANGE OF MODERN WEAPONRY
1. Cobra helicopter gunship
2. Artillery guns
3. Light pick-up troop transporter
4. Infantry armed with assault rifle
5. Tanks are also available but will not be used extensively
6. F-16 fighter jet
What is the manpower of the army versus the Taliban?
TALIBAN ARE LIGHTLY ARMED BUT HIGHLY MOBILE AND ADAPTABLE
1. Main weapon: AK-47 assault rifle
2. Improvised explosive devices can be deadly
3. Toyota Hi Lux pick-up light transport. Here Taliban guerrillas are armed with RPGs
There are two divisions - or about 30,000 soldiers - of Pakistan's army already deployed on the edge of Waziristan. In addition the Frontier Corps - the paramilitary force made up of recruits from tribal areas - is likely to support army operations.
The number of militants is far harder to estimate. An army spokesman recently estimated their strength at between 10,000 and 20,000 fighters.
In South Waziristan Hakimullah Mehsud heads what is thought to be the largest militant force with an estimated strength of more than 15,000 armed men - although the "hard core" of his fighters is much smaller.
The western stretch bordering Afghanistan is the territory of the Ahmedzai Wazir tribe. The current operation is likely to be confined to the Mehsud area.
Analysts say there are also at least several hundred foreign, mainly Uzbek, fighters in South Wazirstan.
What tactics are being deployed?
The army says it has sent its troops and artillery into the region from the north, east and west.
The army appears to be heading towards the Mehsud stronghold of Makeen.
If the military goes in with full force, the militants are likely to disperse rather than attempt to hold territory, analysts say.
But so far they have been reported to be putting up resistance. Militants have also destroyed an important telecommunications tower.
Analysts say the militants will almost certainly engage in guerrilla warfare. With their knowledge of the terrain they are likely to launch ambushes as has been the case in previous assaults.
Reports say the militants are already using tunnel networks and booby traps.
But a lot depends on the tactics the army deploys from now on. Previously, the military has not had a clear strategy when venturing into Waziristan.
It remains to be seen if that is the case this time round.
The army would have to hold the roads and the main towns. Currently the Mehsud-dominated centres of Ladha, Makeen and Sararogha are virtual no-go areas.
A primary military target would be to take control of the heights and put up outposts.
And they are likely to continue their policy of going after mid- and high-ranking Taliban commanders.
What has happened in past encounters?
Waziristan has a long tradition of resisting outside interference.
WAZIRISTAN ASSAULTS AND PEACE DEALS
March - April 2004: Two-week assault where military suffered heavy casualties, ending in peace deal with militant Nek Mohammad
January - Feb 2005: Peace deal with Taliban leader Baitullah Mehsud ends significant army presence there
December 2007 - January 2008 - Army operation in Mehsud area partially successful but ended in peace deal with Baitulalh Mehsud
October 2009 - Army launches offensive
From the 1860s onwards, British forces made gruelling expeditions into the area following audacious attacks from Waziristan tribesmen in British-ruled territory.
More than a century later, it is no easier for the Pakistani army.
In 2004 the Pakistani army suffered heavily at the hands of Wazir-affiliated militants.
There is a possibility that a military offensive against the Mehsud group in South Waziristan could draw into the conflict militant groups based in the Wazir tribal areas of South and North Waziristan.
These groups are currently part of an al-Qaeda-affiliated network who have so far concentrated on fighting inside Afghanistan. They have "peace agreements" with the Pakistani army.
Can Pakistan hold on to South Waziristan?
Even if Pakistan's military is successful this time round against the militants, it will still be faced with the challenge of ensuring they do not get a foothold in the region again.
Mehsud tribesman are sometimes considered to be sympathetic to the Pakistani Taliban. Many are seen as unsupportive of the government offensive.
Taliban leader Hakimullah Mehsud and his predecessor Baitullah Mehsud are both of the Mehsud clan.
Analysts suggest that the army may have to maintain a significant presence in the region in order to preserve a military advantage. This would be a significant commitment of resources.
Officials from the region also suggest that this may be the time to integrate the semi-autonomous tribal areas into the rest of the country.
But Pakistan continued the British tradition of indirect government for a reason: the people of these areas feel independent in many respects.
Another way of seeking to foster stability in the area may be to pour in development and reconstruction funds.