Pakistani jets pounded militant hide-outs along the Afghan border overnight as hundreds of thousands of civilians fled South Waziristan in anticipation of an expected government offensive there, government officials said Wednesday.

Government officials have threatened an operation in the lawless border area for months, but they said a string of recent suicide bombings blamed on the Taliban has strengthened their resolve to engage in what will likely be a long and bloody confrontation.

About 200,000 people have fled South Waziristan since August, moving in with relatives or renting homes in the Tank and Dera Ismail Khan areas in an exodus that has continued in recent days, a local government official said. About half of them registered with the government as displaced people, the official said, speaking on condition of anonymity because he was not authorized to speak to the media.

While there are no recent census data from South Waziristan, estimates of the population hover around 500,000.

Military jets have been hitting suspected Taliban strongholds in the region for weeks. The airstrikes have grown more frequent in recent days in what appears to be an effort to soften up the militants ahead of a ground assault.

The military launched a new wave of air attacks across the militant heartland late Tuesday and early Wednesday, hitting at least five different areas, two intelligence officials said. One attack on a hide-out in Makeen killed three insurgents, and another in Barwand killed six, they said. Meanwhile, forces in an army camp in Razmak shelled militant positions in the surrounding mountains, they said.

The officials spoke on condition of anonymity because they were not authorized to speak to the media.

Independent confirmation of the attacks was not available. The army has barred reporters from the region.

Pakistan has been hit by four major terrorist attacks over the last 10 days, including a suicide bombing of a U.N. office in the capital, Islamabad, and a 22-hour siege over the weekend of the army's headquarters just outside the capital.

The military says 80 percent of the attacks in Pakistan are planned from South Waziristan but that militants from the Punjab province in the heart of the country helped the Taliban with the assault on army headquarters.

The U.S. has encouraged Pakistan to take strong action against insurgents who are using its soil as a base for attacks in Afghanistan, where U.S. troops are bogged down in an increasingly difficult war. But a push into rugged South Waziristan could be difficult for the army, which was beaten back on three previous offensives into the Taliban heartland there and forced to sign peace deals.

An army spokesman declined to say when the South Waziristan offensive would begin and gave no indication it was imminent.

The new airstrikes came as Pakistan's foreign minister visited Washington to persuade U.S. officials to change the terms of a U.S. aid bill. The legislation promises $1.5 billion a year over the next five years — but on the condition that Pakistan's weak, U.S.-backed civilian government maintain effective control over the military, including its budgets, the chain of command and top promotions.

Democratic Sen. John Kerry, who co-sponsored the aid bill, sought to soothe anger in Pakistan, saying lawmakers would provide written assurances that the United States has no intention of interfering with Pakistan's sovereignty.

The objections to the bill have driven a wedge between the military and the government in Islamabad over an aid drive that was supposed to show American support for the country as it battles the insurgents.