Soldiers fought for control of the Pakistani Taliban chief's hometown Wednesday, pressing forward with a major offensive targeting an insurgent stronghold along the Afghan border, authorities said.

The battle raged as intelligence officials said suspected U.S. missiles killed two militants in a neighboring region — a potentially troubling strike because it hit territory controlled by another militant faction the army has coaxed into neutrality during its offensive.

The five-day-old operation in South Waziristan is considered a critical test of the nuclear-armed country's campaign against Islamist extremists blamed for soaring attacks at home and on Western forces in neighboring Afghanistan.

On Tuesday, twin suicide bombings killed six people at Islamabad's International Islamic University in apparent retaliation for the offensive. All educational institutions in the country were closed Wednesday, showing the militants' ability to disrupt daily life.

The military is advancing on three fronts in South Waziristan. The fight for Kotkai town is symbolically key because Taliban chief Hakimullah Mehsud and a top deputy, Qari Hussain, hail from there. It also lies on the way to the major militant base of Sararogha.

An army statement Wednesday said forces were engaged in "intense encounters" in heights surrounding Kotkai and had secured an area east of it. Two intelligence officials said troops had secured parts of the town and also destroyed houses belonging to Mehsud and Hussain in controlled explosions, but army spokesman Maj. Gen. Athar Abbas denied that late Wednesday, saying most of the fighting was on hillsides and the outskirts of the town.

Security forces also cleared Khaisura, a village on another front in the offensive, according to the army statement. Heavily fortified bunkers were found, some with two-meter thick concrete walls, the army said.

It reported three more soldiers were killed, bringing the army's death toll so far to 16, while 15 more militants were slain, bringing their overall death toll to 105.

It is nearly impossible to independently verify information coming from South Waziristan because the army has closed off all roads to the region. Analysts say both sides have exaggerated successes and downplayed losses in the past.

The missile strike Wednesday targeted Spalaga, a village with at least 1,000 homes in the North Waziristan tribal region. Two intelligence officials said at least two suspected insurgents were killed. Their exact identities were not immediately known.

All the intelligence officials interviewed Wednesday requested anonymity because they also were not authorized to speak to media.

The U.S. has launched scores of missiles in South and North Waziristan over the past year, including one that killed former Pakistani Taliban chief Baitullah Mehsud in August, but the latest strike was especially sensitive.

It hit territory controlled by Hafiz Gul Bahadur, a militant leader who has focused on battling U.S. and NATO troops in Afghanistan, unlike the Mehsud-run Pakistani Taliban, who attacked targets inside Pakistan.

In a classic strategy of divide and conquer, the army has convinced Bahadur and other insurgent groups in the tribal belt to stay neutral as it fights Mehsud's faction in South Waziristan.

The missile strikes, which have long angered ordinary Pakistanis and motivated militant fighters, could stir fury among Bahadur's insurgents, straining the deals with the army.

"This has the potential of messing up the calculus of the Pakistanis," said Kamran Bokhari, an analyst with Stratfor, a U.S.-based global intelligence firm. "It could broaden the scope of the war for the Pakistanis, which they're not prepared for at this time."

Pakistan routinely condemns the American missile strikes as violations of its sovereignty, but many observers suspect the two countries have a deal allowing the drone-fired attacks. U.S. officials rarely discuss the covert operation, but have said in the past that it has killed several top militant leaders and is too valuable to set aside.

Abbas, the military spokesman, cautioned that the fight in South Waziristan could be long.

"This is a mountainous terrain and therefore the operations tend to be slow," Abbas told the AP in an interview Tuesday. The militants "are very tough fighters. They know the area, terrain. And they are very determined to fight."

Abbas said the military believed that Mehsud and Hussain remain in the region under fire, directing the militants' defenses. That information is based on local informants and communications intercepts, Abbas said.