The CIA is using an arsenal of armed drones and other equipment provided by the U.S. military to secretly escalate its operations in Pakistan by striking targets beyond the reach of American forces based in Afghanistan, U.S. officials said.

The merging of covert CIA operations and military firepower is part of a high-stakes attempt by the Obama administration to deal decisive blows to Taliban insurgents who have regained control of swaths of territory in Afghanistan but stage most of their operations from sanctuaries across that country's eastern border.

The move represents a signification evolution of an already controversial targeted killing program run by the CIA. The agency's drone program began as a sporadic effort to kill members of the al-Qaeda terrorist network but in the past month it has been delivering what amounts to a cross-border bombing campaign in coordination with conventional military operations a few miles away.

The campaign continued Saturday amid reports that two new CIA drone strikes had killed 16 militants in northwest Pakistan, following 22 such attacks last month.

The strategy shift carries significant risks, particularly if it is perceived as an end-run around the Pakistan government's long-standing objections to American military operations within its domain.

Indeed, the surge in drone strikes over the past four weeks has to a large extent targeted elements of a network led by Jalaluddin Haqqani, a militant regarded as a close ally of Pakistan's powerful Inter-Services Intelligence directorate.

Officials said last week that some of the recent strikes have also been aimed at disrupting al-Qaeda terror plots targeting Europe. A U.S. official said the State Department was weighing whether to issue an alert that would caution Americans to be "vigilant" when traveling in Europe - guidance that could come as soon as Sunday.

The U.S. military quietly has been providing Predator and Reaper drones, as well as other weaponry, to the CIA in an effort to give the agency more capacity to carry out lethal strikes in Pakistan, American officials said.

"Increasing the operational tempo against terrorists in Pakistan has been in the works since last year," a U.S. official said. "The CIA sought more resources to go after terrorists in Pakistan, which the White House strongly supported."

The official added that Defense Secretary Robert Gates and CIA Director Leon E. Panetta "worked closely together to expand the effort. The foundation for the latest intensification of strikes was laid then, and the results speak for themselves."

Although President Obama's announcement in December of the results of a U.S. strategy review in the region focused on deployment of 30,000 additional troops to Afghanistan, officials said the months-long evaluation centered largely on the need to eliminate insurgent sanctuaries in Pakistan. In late November, Obama wrote a personal letter to Pakistani President Asif Ali Zardari offering an expanded partnership and bluntly warning that continued ambiguity in Pakistan's relationship with the militants would no longer be tolerated. If the Pakistani military did not take more forceful action, Obama warned, the United States would be forced to act.

That message was reinforced last spring after intelligence indicated that the failed Times Square bomber had been trained in Pakistan. Panetta and National Security Adviser James L. Jones traveled to Pakistan to make clear that the United States was dissatisfied with Pakistan's efforts.