The clashes in the lawless South Waziristan region come as President Pervez Musharraf, a key US ally, faces international pressure to get tough on extremists who have regrouped in Pakistan's tribal-run regions since 2001.

Uzbeks, Chechens and some Arab militants have traded rocket and mortar fire for two days with pro-government tribal forces led by a former Taliban commander after a tense ceasefire broke down Thursday, officials said.

The Pakistani government "is not intervening," a top security official told AFP on condition of anonymity.

"We hope this onslaught against foreign militants will help reduce cross-border activity. The foreigners were involved in this cross-border activity," the official said.

"This is a decisive battle for us."

Interior Minister Aftab Sherpao told AFP late Friday that 56 people were killed on Thursday and Friday, 45 of them foreigners, after fighting "intensified after peace talks failed."

"Tribes are insisting on their demand that these people either surrender or quit the area," Sherpao said.

The al-Qaeda militants numbering around 500 were effectively under siege as all roads to the areas where they are dug in are controlled by tribal commander Mullah Nazir, who is said to have around 1,500 men, residents said.

Last week the government said clashes in South Waziristan left 160 people dead, again mostly Chechens and Uzbeks. Local sources put the toll lower but the figures could not be independently verified.

Officials said the tribesmen's efforts to drive out the rebels vindicated Islamabad's policy of signing peace deals in the tribal belt instead of sending in government troops as it has in the past, with little success.

Pakistan inked pacts with pro-Taliban tribal militants in South Waziristan in 2005 and neighbouring North Waziristan last year, under which it withdrew many soldiers while the tribes agreed to curb attacks in Afghanistan.