(CNN) -- The United States has escalated its unmanned aircraft strikes at militant targets in Pakistan since seven Americans were killed in a December 30 suicide attack at a CIA base in eastern Afghanistan, statistics from two informed research outlets show.
And analysts believe "revenge" could be a top motivator.
A forthcoming study from the New America Foundation, a public policy institute, said there have been 64 strikes since President Obama took office, 51 in 2009 and 13 in 2010. Fourteen of them occurred since the late December CIA suicide attack, it said.
There were 45 such attacks during the Bush administration, with most occurring since August 2008, said Peter Bergen, a fellow at the foundation and CNN terror analyst, and Katherine Tiedemann, a foundation policy analyst.
Bergen cannot say definitively why the drone attacks have increased, but he cites a revenge factor, saying that U.S. forces are upset and want retribution for the brazen bombing and have cranked up strikes on military targets in the tribal regions of Pakistan.
"The people who died in this suicide attack were involved in targeting people on the other side of the border," said Bergen.
The Long War Journal, an online publication that charts data for U.S. airstrikes against al Qaeda and the Taliban in Pakistan, released similar statistics as well on its Web site.
And Bill Roggio, editor of the journal, told CNN he also believes "there was a revenge factor."
"What we saw after December 30 was really unprecedented," Roggio said. "They had to do two things. They had to show that the attack didn't hurt their ability to target [militants] and that they still had the capacity to do so."
The journal says the air campaign "remains the cornerstone of the effort to root out and decapitate the senior leadership of al Qaeda, the Taliban, and other allied terror groups, and to disrupt both al Qaeda's global and local operations in Afghanistan and Pakistan."
The U.S. military routinely offers no comment on reported attacks by the pilotless aircraft, but officials say the airstrikes are conducted by Americans.
The United States is the only country operating in the region known to have the ability to launch missiles from remote-controlled aircraft.
Strikes have been launched from both Afghanistan and Pakistan, Bergen and Tiedemann said.
The latest such strikes occurred on Tuesday, when unmanned aircraft struck four villages and killed at least 29 people in North Waziristan.
The December 30 suicide bomber, a Jordanian, killed seven CIA officers and contractors and a Jordanian intelligence official at Forward Operating Base Chapman.
The Pakistani Taliban claimed responsibility for that attack.
It was carried out to avenge the death of Pakistani Taliban leader Baitullah Mehsud, who died in a suspected U.S. drone strike last year, according to al Qaeda's commander of operations in Afghanistan, Mustafa Abu Yazid.
Now, the Pakistani military has been looking into reports that Hakimullah Mehsud, the new Pakistani Taliban leader -- who had been the target of drone attacks -- died in one last month.
Pakistani state broadcaster PTV reported he was wounded in January, and that he died and was buried last week. A Taliban source denied the report to CNN, saying that Mehsud has simply gone "underground" after being targeted by drone attacks.
Pakistani military spokesman Maj. Gen. Athar Abbas and U.S. counterterrorism officials said they cannot confirm Mehsud's status.