Islamabad: Pakistani Taliban fighters are moving from the country's tribal northwest to the commercial capital of Karachi to escape drone attacks and military action, a US think tank said.

"Militant groups have long considered Karachi a safe location because it is unlikely the city would ever face a major military operation," the Combating Terrorism Centre, which is part of the US Military Academy in West Point, New York, said in a report. The report is scheduled to be released this week.

Karachi, a city of 18 million people, houses the stock exchange, central bank and offices of global corporations including London-based Standard Chartered and Rotterdam-based Unilever. It contributes more than 70 per cent of Pakistan's tax revenue, according to the local government.

"Taliban are not close to overtaking the city", which has "a powerful and liberal civil society", according to the report. "Nevertheless, if left unchecked, the growing influence of the Taliban in Karachi could spark violent clashes and eventual destabilisation, which would have powerful ramifications for Pakistan."

Largely spared the guerrilla bombings that have surged in other cities since the army began an offensive against the Taliban militants, at least 43 people were killed on December 28 in a bomb attack on a religious procession in Karachi.

It was the deadliest bombing in the city since 170 people were killed in an attack on slain leader Benazir Bhutto's homecoming procession in October 2007.

About 28,000 troops are fighting the Taliban guerrillas in South Waziristan, 917 kilometres northwest of Karachi, and other tribal regions bordering Afghanistan.