Pakistani intelligence officials say a U.S. drone strike has killed four militants in the country's northwest, the third such attack in less than two days.

Officials say missiles struck a vehicle Friday as it traveled near the town of Miran Shah in the North Waziristan tribal region. The identities of those killed were not immediately known.

The day before, a drone strike in the same region killed a ranking member of the militant Haqqani network. A U.S. official in Washington described Janbaz Zadran, also known as “Jamil,” as the senior most Haqqani leader in Pakistan to be taken off the battlefield.

The United States does not publicly acknowledge the use of drone strikes against Taliban and al-Qaida-linked militants in Pakistan's northwest. Pakistani officials have protested the attacks as a violation of the country's sovereignty.

Pakistan has so far resisted U.S. pressure to launch an offensive against militants in North Waziristan, saying the military needs to solidify gains elsewhere in the region.

The Haqqani network, which has launched numerous attacks in Afghanistan, is believed to be based in North Waziristan.

U.S. officials have accused Pakistan's military spy agency of supporting the group, a charge Pakistan denies.