The Taleban are leading the insurgency
There has been a huge increase in violent attacks in Afghanistan in recent months, particularly in the south where Nato forces are helping the Afghan government to extend its authority.
The government blames most of the violence on what it calls "enemies of Afghanistan" - shorthand for the Taleban and their al-Qaeda allies.
Both groups appear to be stronger than they have been since before the fall of the Taleban administration in 2001.
Pakistan continues to deny Afghan allegations that it is sheltering and aiding the Taleban.
But it is becoming increasingly difficult to establish with any certainty who is behind some of the violence and exactly who supports the insurgency.
The top UN envoy for Afghanistan, Tom Koenigs, recently alleged that the Taleban and their al-Qaeda allies were being backed by foreign money and terror networks.
But he also said the insurgency includes the children of Afghan refugees who have been educated in Pakistani religious schools or madrassas, as well as young men from Afghanistan with few prospects.
Some say the Taleban's current strength stems partly from their intimidation of the local population, but also from the fact they can pay young Afghan men more than the Afghan army can pay them.
The militants are behind a spate of suicide attacks
However, the situation remains murky and complex, as Paul Rogers of Bradford University explains.
"As far as we can tell, it's elements of the old Taleban leadership who are at the forefront of what is happening now. But they are overseeing a very diffuse group.
"Many of them would describe themselves as adherents to the Taleban outlook, but it includes people who are essentially allied to local warlords.
"It certainly includes small landowners who are concerned about losing their capacity to grow opium poppies because of the eradication campaigns that are on."
The Taleban's offers to protect farmers from eradication campaigns will have boosted their popularity in major poppy-growing provinces like Helmand.
The powerful drugs trade is undoubtedly intertwined with the current violence.
The insurgency is closely linked to opium growing
Local power holders who feel marginalised may find themselves allied to the Taleban, at least in the short term.
In some areas it's difficult to distinguish between attacks by the Taleban and those by other radical Islamic groups or individuals.
These include Hezb-e Islami, headed by former Prime Minister Gulbuddin Hekmatyar, or those loyal to Jalaluddin Haqqani, a former mujahideen leader who also served in the Taleban government.
The situation is further complicated by a complex web of shifting allegiances, tribal, ethnic and local rivalries and feuds within Afghan society.
Afghans have been known to denounce rivals or enemies as members of the Taleban for political or economic gain.