Latest drone strike in Pakistan kills 15

Drone strikes in Pakistan have long been a thorn in U.S.-Pakistani relations, which have taken a markedly downward turn in the past year.

Islamabad was outraged last May when U.S. Navy SEALs went deep into Pakistani territory to kill Osama bin Laden. U.S. officials, meanwhile, openly accused Pakistan of knowing where the terrorist leader was hiding.

But after 24 Pakistani soldiers were killed by NATO soldiers on the Afghan-Pakistani border in November, Pakistan shut down the NATO supply lines into Afghanistan.

The United States has sought to reopen those lines, but negotiations have not been successful thus far, with monetary demands from Pakistan.

While the Pentagon has said the shutdown lines have not affected NATO transport in Afghanistan — though the cost has gone up sharply using alternative routes — the supply lines will be important as U.S. forces begin withdrawing from Afghanistan.

Pakistani President Asif Ali Zardari was a last-minute invite to the NATO Summit in Chicago last month, where some speculated a deal might have been reached on the supply lines, but that deal did not come even after Zardari met with President Obama.

But with U.S.-Pakistani negotiations ongoing, the continued drone campaign likely shows that the United States has no signs of relenting.

A senior U.S. official told The New York Times that the recent offensive was not about sending a message, but had more to do with a run of good, clear weather.