(CNN) -- A suspected U.S. drone strike in Pakistan's tribal region killed four suspected militants Friday, intelligence officials said.
It was the latest in a spate of suspected drone attacks that the United States has carried out in Pakistan since U.S. forces killed al Qaeda leader Osama bin Laden in the early morning hours of May 2.
The suspected drone fired two missiles on a vehicle in the area of Miran Shah of North Waziristan, a region near Pakistan's border that is rife with Islamic extremists, two intelligence officials said. They asked not to be named because they were not authorized to speak to the media.
Suspected U.S. drone strikes, a source of tension between the two nations, have increased in pace in Pakistan since bin Laden's death.
The United States has carried out six suspected drone strikes in Pakistan in the past 15 days, according to a CNN count based on information from Pakistani intelligence sources. That works out to an average of one strike every 2.5 days.
From January 1 through May 5, by contrast, the United States conducted 20 suspected strikes, an average of one drone strike every six days, according to CNN's count.
The recent increase, however, probably is not due to intelligence gained from bin Laden's compound, Bill Roggio, a military affairs analyst and editor of the Long War Journal, has said.
"This uptick is not unusual from a recent historical perspective, he said. "What has happened, since the bin Laden raid, is that the U.S. has not felt pressured to dial back the attacks due to Pakistani sensibilities."
The United States has conducted a string of drone strikes in a fairly short time period before, he said, while at other times several weeks have passed without such a strike.
He attributes a lull in the first months of this year to tension between the United States and Pakistan over the arrest of CIA contractor Raymond Davis and other disputes between the countries' intelligence services.
Authorities in Pakistan detained Davis after he shot and killed two men in what he described as a case of self-defense. Davis was released after a payment was made to the men's families.