Pakistan troops prepare to leave to patrol around Bannu, a town on the edge of Pakistan's lawless tribal belt Waziristan, on Saturday. (Ijaz Muhammad/Associated Press)Thousands of civilians in an insurgent-held region of Pakistan fled for safety as the country's army fought militants in the third day of a military campaign.

Pakistani troops fought insurgents on three fronts as fighter jets continued to bomb militant positions in the region of South Waziristan. The semiautonomous region is believed to be a base for Taliban and al-Qaeda-linked insurgents to carry out attacks on Pakistan, Afghanistan and targets in the West.

Up to 150,000 civilians left in recent months after the army made clear it was planning an assault, but as many as 350,000 remain, and reports from the region suggest a steady stream of civilians are lining up at checkpoints to evacuate the area.

Authorities say as many as 200,000 people may flee in the coming weeks.

Residents fleeing Sunday suggested militant resistance to the army was tougher than in the Swat Valley, a region also in the northwest where insurgents were overpowered earlier this year.

On Monday, Pakistani intelligence officials revealed that the army had reached prior agreements with two militant commanders — whose supporters are believed to be fighting U.S. forces in Afghanistan — to stay neutral during the assault.

That could trigger concern in Washington, which has been pushing Islamabad to launch the offensive, seen as the most crucial yet against militants who are in control of a large swath of Pakistan's northwestern frontier region.

Also on Monday, U.S. central command chief Gen. David Petraeus met Pakistan's prime minister and army chief in the capital. U.S. Senator John Kerry also met the two Pakistanis to try to ease tensions over an American aid bill that has caused a rift between Pakistan's army and the civilian government.

Both the Pakistani army and the Taliban have claimed early victories in the fighting. The army claimed Sunday that 78 militants and nine soldiers have been killed in the offensive, which began Saturday. Intelligence officials said eight more militants were killed Monday in the Khaisur area of South Waziristan.

The Taliban said its fighters inflicted "heavy casualties" on the army.

Fighting on 3 fronts: intelligence officials

Intelligence officials said fighting was going on Monday close to Jandola, Razmak and Wana, three towns where the army has bases.

A Pakistani family, which fled due to military offensive against al-Qaeda activists and Taliban militants, passes through a checkpoint on the outskirt of Bannu, a town on edge of Pakistani's tribal region of Waziristan. (Ijaz Muhammad/Associated Press)

It is nearly impossible to independently verify what is actually happening, however, because the Pakistani military is blocking access to the region and surrounding towns.

Some 30,000 troops are up against an estimated 10,000 Pakistani militants and about 1,500 foreign fighters.

For Pakistan, the offensive is a crucial effort in a campaign to rid the country of militant insurgents who have been behind a series of brazen attacks on different sites across Pakistan in the past weeks, including the army headquarters in Rawalpindi and the police training school in Lahore. The assaults killed 175 people.

Pakistani officials say they believe some 80 per cent of attacks against the military originate from South Waziristan.

The Pakistani army has had little success in previous attempts to root out militants. Three times since 2004 the country's troops have been beaten back from the mountainous region.

In recent weeks, the army has been cutting off possible escape routes for militants and softening targets with a series of air strikes in advance of the offensive.

With files from The Associated Press