Pakistan on Thursday sent paramilitary troops to a district virtually taken over by the Taliban, a day after Washington said Islamabad had abdicated to the militants by agreeing to impose Islamic law in the region.

Around 100 paramilitary troops had been deployed in Buner district, not far from Islamabad, police said. Soon after they arrived, militants attacked their convoy, killing a policeman escorting them, said Arsala Khan, a deputy police superintendent.

'A platoon of the Frontier Corps has arrived in Buner to help police maintain security in the district,' Khan told Reuters.

Surging violence across Pakistan and the spread of Taliban influence in the country's northwest has revived concerns about the stability of the nuclear-armed state, which is crucial to US efforts to stabilise neighbouring Afghanistan.

After failing to quell the Taliban through force, President Asif Ali Zardari last week approved enforcement of Islamic sharia law in the Swat valley and adjoining areas despite criticism from Western countries and Pakistani liberal and rights groups.

US Secretary of State Hillary Clinton said on Wednesday the government had abdicated to the Taliban by agreeing to the Swat deal, adding the country now posed a 'mortal threat' to the world.

The chairman of the US Joint Chiefs of Staff, Mike Mullen, met Pakistan's army chief General Ashfaq Kayani and other military officials and discussed security issues, a military official said without giving details. Mullen arrived in Pakistan on a brief visit on Wednesday.

Within days of the government's announcement of the imposition of Islamic sharia law in Swat, 125 km (80 miles) northwest of Islamabad, militants forced their way into nearby Buner, closer to the capital Islamabad. They said their aim was to push their harsh version of Islam across the country.

Residents said the Taliban had occupied police stations in Buner and that gun-totting fighters were roaming market places urging people to support their efforts to impose Islamic law.

Prime Minister Yousaf Raza Gilani reiterated on Thursday that the government had agreed to Islamic law on the advice of a secular party that leads the provincial government, but it could review the pact if peace was not restored.

Politicians who pushed the government to enforce sharia law in Swat have even begun expressing worries about the growing clout of the Taliban.

'If the Taliban continue their advances at the current pace they will soon be knocking at the doors of Islamabad,' Fazl-ur-Rehman, head of the Jamiat-e-ulema-e-Islam, the country's largest Islamic party, told parliament on Wednesday.

Militants earlier on Thursday torched seven trucks carrying fuel to Western forces in Afghanistan on the outskirts of the main northwestern city of Peshawar, police added. - Reuters