TANK, Pakistan, March 31 (Reuters) - Al Qaeda-linked militants and Pakistani tribesmen fired rockets, mortar shells and automatic weapons on Saturday in a region where officials say up to 177 people have been killed since last week.

The fighting showed the foreign militants, most of them Uzbeks from Central Asia, had alienated tribesmen who had earlier sheltered them in Pakistan's South Waziristan region after U.S. backed forces chased them out of Afghanistan in late 2001.

Two children were killed overnight when a mortar bomb hit their home in Ghawakhawa, a village a few kilometres (miles) west of Wana, the main town in South Waziristan, witnesses said.

Interior Minister Aftab Ahmed Khan Sherpao said more than 50 people had been killed on Friday during clashes between Islamist militants and local Pashtun tribesmen.

Witnesses said the estimate was on the high side, but even by their reckoning the fighting has taken a heavy toll.

A resident of Shin Warsak, the village where fighting is concentrated, said he saw the bodies of 21 dead foreigners.

"Sporadic heavy fire continued throughout the night, but it has become more intense now in Shin Warsak," Noor Ali, another resident, told Reuters.

The clashes began after the Uzbek militants tried to assassinate a pro-government tribal leader earlier this month, and flared again on Wednesday after attempts to broker a truce broke down.

The tribesmen are demanding the militants lay down their arms and leave the area. The government views the turnaround as a success for its strategy of trying to win over the tribesmen and isolate the foreign interlopers.

Having lost more than 800 troops fighting pro-Taliban tribesmen and al Qaeda in North and South Waziristan, the government struck peace deals with militant tribesmen last year and in 2005.

Critics said the pacts risked creating militant sanctuaries in the two semi-autonomous tribal regions, but the clashes in March showed the tribesmen could be finally keeping their end of the bargain.

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