Islamabad, Pakistan (CNN) -- A suspected U.S. drone fired six missiles into a compound in North Waziristan, killing 13 suspected militants Friday, according to a Pakistani intelligence official and a local government.
Twelve others were injured, said the officials, who asked not to be named because they were not authorized to speak to the media. The missiles were fired at a suspected militant compound in Maizer Madakhel, a village in North Waziristan.
The aerial attack came hours after a similar drone strike killed three others in the same northwest Pakistani region Thursday. That attack targeted a compound housing militants, two Pakistani intelligence officials said.
Pakistan is gearing up for military operations in North Waziristan, which security analysts have described as a haven for various factions of Afghan and Pakistani Taliban and al Qaeda militants.
Although the United States is the only country in the region known to have the ability to launch missiles from drones, which are controlled remotely, U.S. officials normally do not comment on suspected drone strikes.
Before the latest two attacks, 37 of 39 reported strikes this year have hit targets in North Waziristan, said Peter Bergen, CNN's national security analyst.
Last week, the U.N.'s senior official for extrajudicial executions, Philip Alston, said the United States should explain the legal rationale for the drone strikes in northwest Pakistan, which he characterized as "a vaguely defined license to kill" that has created "a major accountability vacuum."
Alston also urged the Obama administration to disclose the number of civilians killed in the drone strikes.
The civilian death toll has angered Pakistanis, less than a tenth of whom support the strikes, Bergen said.
According to a count by the New America Foundation, a Washington-based think tank where Bergen is a fellow, since 2004 the drone program in Pakistan has reportedly killed at least 976 people, a third of whom were not militants.