Pakistan braced Tuesday for more militant attacks ahead of an anticipated offensive against a Taliban stronghold, as the insurgents said they bombed a U.N. relief agency because international aid work was not in "the interest of Muslims."

The suicide bombing Monday at the World Food Program headquarters in Islamabad killed five people, prompting the U.N. to temporarily shut all its offices across the country.

The attack proved the Taliban retained the ability to launch deadly strikes in the heart of Pakistan despite government hopes that the Aug. 5 killing of their leader Baitullah Mehsud in a CIA drone attack and recent military successes in the Swat Valley would send the group spiraling into chaos.

Pakistani officials have said they are prepared to launch another offensive to rout the Taliban from their mountain redoubts in South Waziristan. A media report last week said a major ground offensive was imminent, and an AP reporter in the area Sunday saw Taliban fighters taking up positions and villagers fleeing.

Such an offensive would likely come at a high price for the military. The army has been beaten back there three times since 2004 and analysts say 10,000 well-armed militants, including foreign fighters, are dug in around the region.

Helicopter gunships, jet fighters and artillery batteries pounded suspected militant hide-outs in South Waziristan on Tuesday, killing two militants and seven other people, intelligence officials said, speaking on condition of anonymity because they were not authorized to speak to the media. They said the army was trying to establish whether the seven unidentified victims were militants.

The military launched the strikes in response to a Taliban attack on two military bases, the officials said.

Interior Minister Rehman Malik said the government was already targeting the Taliban in South Waziristan and "if needed, further action shall also be taken at an appropriate time" against militants in other areas along the Afghan border.

Washington has pressed Pakistan to crack down on the militants, and on Tuesday the top U.S. commander in Afghanistan, Gen. Stanley McChrystal, met Pakistan military chief Gen. Ashfaq Parvez Kayani in Islamabad. The Obama administration is debating whether to add up to 40,000 more troops to fight the resurgent Taliban in Afghanistan, but says it cannot win there unless Pakistan does more to fight militants on its side of the border.

The Taliban said they would repel any offensive against their strongholds.

Spokesman Azam Tariq said the Taliban claimed responsibility for the attack on the U.N. office and vowed to carry out more attacks.

"The U.N. and other foreign (aid groups) are not working in the interest of Muslims. We are watching their activities. They are infidels," he told The Associated Press by telephone from an undisclosed location.

He said the Taliban would not attack Muslim relief groups, but that future targets would include Pakistani security officials, government offices and American installations.

Malik said the country "should expect a few more" bombings.

The attack on the heavily fortified World Food Program compound prompted the U.N. to temporarily close its offices in the country, though it said its Pakistani partner organizations would continue distributing food, medicine and other humanitarian assistance. The world body said it would reassess the situation over the next several days.

World Food Program spokesman Amjad Jamal defended the agency's work as "totally humanitarian."

"We provide food. Our food is for the vulnerable groups, the poor groups who cannot afford one meal a day," he said.

Pakistani religious scholar Mufti Muneebur Rehman disputed the Taliban claim that international aid work was against Islam.

"Helping somebody in need is one of the best traits of Islam," he said. "A good Muslim would be the first to help any non-Muslim in trouble."

Prime Minister Yusuf Raza Gilani said those killed in the bombing Monday were serving a "noble cause."

"Such cowardly terrorist acts will never weaken our resolve to fight against this scourge," he wrote in a letter to U.N. Secretary-General Ban Ki-moon.