Islamabad ? Islamic militants mounted their fourth attack against a Pakistani target in a week, this time detonating a suicide car bomb in a crowded bazaar that killed 41 people in the Shangla District on the edge of the Swat Valley, where the Pakistani military had said it crushed the insurgency.

The latest attack, carried out by a bomber who local security officials said was 12 or 13, comes as Pakistan’s military accelerates a planned offensive against Islamic extremists in the country’s South Waziristan region, which is also a refuge for the Taliban and other militant groups battling the U.S.-led international force in neighboring Afghanistan.

A senior military official, who couldn’t be named because of the sensitivity of the issue, said the army would launch the operation “in hours,” adding that a weekend attack on the country’s military headquarters in Rawalpindi forced plans to be hastened. Other officials, however, suggested that a ground assault remains days away.

Washington has pressed Pakistan to take action in Waziristan, the heart of the country’s Islamic insurgency and a refuge for Afghan insurgents and al Qaida. An estimated 15,000 battle-hardened Pakistani Taliban are holed up in South Waziristan, where the mountainous terrain favors guerrilla warfare.

Pakistan has fought at least three military offensives in South Waziristan since 2004, but each time, the military has been forced to retreat and leave the Taliban in control.

As the Obama administration seeks greater Pakistani support for its fight against al-Qaida and the Taliban, conditions Congress included in a bill it’s passed to provide $7.5 billion in aid to Pakistan are straining relations between the two countries.

Bowing to pressure from the country’s military and its opposition parties, the government of President Asif Ali Zardari appears ready to demand that Congress rewrite the legislation to remove demands that Pakistan take action against terrorism and nuclear proliferation and maintain civilian control over the military. Last week, Pakistan’s army chief expressed “strong concern” over the bill, which he said interfered in national security matters.

Pakistani Foreign Minister Shah Mehmood Qureshi left for Washington on Monday to convey the “feelings” of his country to Congress and the White House.

“Pakistan will make no compromises in its sovereignty or allow micro-management (of the country),” he said.

It wasn’t clear, however, whether Qureshi’s visit is intended mostly for domestic consumption or whether he’ll attempt to convince Congress to rewrite legislation that’s awaiting President Barack Obama’s signature, which seems unlikely.

It also remains to be seen whether the latest wave of terrorist attacks, which have killed more than 100 people, will prompt Pakistan to step up its campaign against Islamic militants.