Pakistani forces battled al Qaeda-linked militants yesterday in a fifth day of fighting in a remote tribal region bordering Afghanistan, where several army posts came under rocket attack, witnesses said.

Artillery fire boomed in the Shakai area of South Waziristan, 400 km (250 miles) southwest of Islamabad, where Pakistani forces were trying to flush-out foreign and local militants from their mountain hideouts, witnesses said.

?Our houses shook because of the artillery fire all night,? said one resident in Wana, the main town of South Waziristan. The army was hitting targets in the Shakai area. Militants fired rockets at two remote Pakistani posts near the Afghan border on Saturday night, but there were no reports of casualties, residents said. The posts are some distance away from the battle-zone.

More than 50 combatants ? 35 militants and 15 soldiers ? were killed in the first two days of fighting, the army said. Since then, the army has not updated the figure but official sources said the number of casualties in the five days of fighting was much higher. Pakistan says up to 600 foreign militants, including Arabs, Chechens and Uzbeks linked to Osama bin Laden?s al Qaeda network, have been hiding out in the semi-autonomous tribal areas, protected by Pakistani tribesmen.

Pakistani forces sent air force jets to bomb militant hideouts on Friday for the first time ? raising the stakes in the war against al Qaeda in the country. In March, Pakistan used helicopter gunships in clashes against the militants in which more than 120 people, including 46 soldiers and 63 militants were killed. No fresh air-strikes were carried out overnight and early yesterday, residents said. Pakistani forces are targeting suspected training camps and safe-houses of militants. The houses of residents thought to be supporting militants are also being destroyed. Top al Qaeda leaders ? including possibly bin Laden ? are believed to be hiding out in Pakistan?s mountainous tribal region.

The US military in Afghanistan has said it has employed a ?hammer and anvil? approach in coordination with the Pakistani military to prevent militants escaping across the border. The Pakistani operation near Wana was launched amid a broad operation by US and Afghan forces across several provinces of southern Afghanistan aimed at improving security for Afghan elections due in September. The US military said on Saturday more than 80 militants had been killed in that operation over the past three weeks. In Pakistan, the army said it launched the latest offensive in the tribal regions after attempts to negotiate an amnesty with tribesmen protecting foreign militants failed.

?We want them to surrender or they will be wiped out,? said a security official speaking on condition of anonymity. ?We have identified 16 more compounds and places in the Shakai area that are being used by militants,? he said. ?They are also being targeted,? he added, declining to give details.

Authorities fear that shadowy Islamic militant groups could launch attacks in other parts of the country in response to the operation in the tribal region.

On Thursday, a Pakistan army commander narrowly escaped assassination when a gun and bomb attack on his convoy killed 10 people in the port city of Karachi. Security has been heightened at Western establishments, sensitive government installations and places of worship in major cities because of fears of more such assaults by militants sympathetic to al Qaeda, officials said.

Pakistan has already witnessed a spate of assaults on religious minorities, top government officials and Westerners. Six months ago, President General Pervez Musharraf survived two assassination attempts that were blamed on al Qaeda-linked militants. Later Musharraf revealed several low-ranking military personnel were also involved.

Hafiz Wazir