The army says that it capturing territory all over South Waziristan
Pakistani troops fighting the Taliban in South Waziristan have surrounded a key stronghold of Uzbek fighters, military officials say.
They say that the town of Kaniguram - one of the largest towns in the area - is also the "operational centre" of the Pakistani Taliban.
The army says its offensive against the militants is "making good progress".
But a US-based rights group warned of "catastrophe" if aid is not allowed in to help civilians trapped in the area.
In a statement released on Thursday Human Rights Watch said that Pakistani authorities should ensure that civilians who cannot escape the fighting should have sufficient access to basic necessities.
The group cites reports of people trying to escape the fighting before the onset of a harsh winter.
Tens of thousands of civilians have fled the conflict zone since hostilities broke out.
The army says that two medical camps have been set up for displaced families and existing basic health units are being upgraded.
The army has declared South Waziristan a closed military zone until the operation ends.
It also announced "substantial successes" on fronts in the Nawazkot and Razmak-Makeen areas, adding that 11 militants and one solider had been killed in the latest fighting. But analysts say that stiff resistance being put up by militants indicate that all is not going to plan for the army.
Journalists have been denied access to the area and so cannot verify army reports of fighting.
Fight to the death
The town of Kaniguram, which troops are currently battling for, has between 85-90,000 residents and is second only to the town of Wana in terms of its population.
The BBC's Syed Shoaib Hasan in Islamabad says that at least 1,500 Uzbek militants are thought to be there.
In the past Uzbek fighters have been led by Tahir Yuldashev, head of the the hardline Islamic Movement of Uzbekistan (IMU).
Mr Yuldashev is believed to have been killed recently, but the Taliban have denied his demise and for the moment there has been no word on a successor.
Our correspondent says that even without a leader, the Uzbeks will know this is a fight to the death for them.
While a few Uzbek militants have been living in Kaniguram for years, most arrived after being evicted from Wana by pro-government Taliban commander Maulvi Nazir in March 2007.
Pakistan's military establishment holds the IMU primarily responsible for the re-orientation of the formerly Afghanistan-focused Taliban towards Pakistan and its security forces, analysts say.
The Uzbeks are said to be the driving force behind the ideology of "fighting the enemy who is closer first" - in this case the Pakistan army.
Our correspondent says that this fact - and the urban nature of the battle - means that fighting in Kaniguram is likely to be intense and casualties high.
The majority of the residents of Kaniguram are of the Burki tribe - who dominate the area. But there are also members of the Mehsud and Wazir tribes.
The town is notable for hosting a substantial number of militants loyal to the Pakistani Taliban led by Hakimullah Mehsud.
Kaniguram itself is surrounded by mountains, the highest of which towers to 12,000 feet. There is a network of tarmac roads connecting it to the rest of the region, but they generally remain blocked in winter.
South Waziristan is considered to be the main sanctuary for Islamic militants outside Afghanistan.
Pakistan launched its offensive after a wave of militant attacks, believed to have been orchestrated from South Waziristan, killed more than 150 people in October.