Islamabad  - Pakistan has ordered the formation of a specialist team of investigators to question a pro-Taliban cleric who negotiated a failed peace pact in the insurgency-hit Swat Valley, officials said Monday.

Sufi Mohammad was arrested in the north-western city of Peshawar Sunday for aiding militants and sabotaging government efforts to stave off violence.

The radical cleric was also accused of encouraging terrorism, and a senior official in North-West Frontier Province, where Swat and Peshawar are located, said cases would be filed against him after an inquiry.

"Federal Interior Minster Rehman Malik has asked the provincial government to constitute a joint investigation team to interrogate Sufi Mohammad," said Nawazish Ali, a spokesman for the ministry.

The team is to be made up of officers from federal as well as provincial security agencies, Ali said.

Mohammad, who was released in 2008 after six years of detention, brokered a peace deal between the government and Islamist rebels in February this year to put an end to nearly two years of armed struggle by the Taliban to enforce strict sharia Islamic law in the region.

Authorities agreed to set up Islamic courts in Swat and nearby areas on assurances that the militants would disarm and stop attacks on the security forces.

But the faltering peace agreement collapsed in April when the militants defied the deal and overran Swat's neighbouring district of Buner, located 100 kilometres north of the Pakistani capital, Islamabad. Mohammad apparently had little control over militants led by his son-in-law, Maulana Fazlullah.

The bold advances and unrelenting expansion of influence prompted the government to launch an offensive against the rebels in late April.

The military said more than 1,700 militants have been killed in the ongoing campaign, which is nearing its end.

Most parts of Swat, a former tourist hub, and its adjoining districts have been cleared, but troops were still fighting remnants in remote mountain areas.

Analysts said they fear the uprising could resurface because none of the top Taliban leaders in Swat have been apprehended or killed in the nearly three-month onslaught, which also left at least 160 soldiers dead.

The fierce clashes displaced around 2 million people, sparking concerns about a humanitarian crisis. However, the refugees have now gradually started returning to their homes in areas opened by the military. (dpa)