The US strikes are part of a flurry of such attacks which could indicate a more aggressive American strategy against insurgents finding sanctuary in Pakistan.
The United States is pressing Pakistan for action against Afghan insurgents in the region, especially the Haqqani network that it says is the No. 1 threat in Afghanistan and receives assistance from the Pakistan army.
Independently of what Pakistan does, Washington may up the tempo of missile strikes or widen their targeting, although either option could strain its already complicated relationship with Islamabad, Pakistani intelligence officials said.
Washington has regularly used drones since 2008 to pummel insurgents and their hideouts in Pakistani tribal regions. U.S. officials do not acknowledge the CIA-led program. Pakistan publicly protests the strikes, which are unpopular in this Islamic nation, but tolerates them in practice.
In the latest attack, drone-fired missiles slammed into a compound near the border town of Angore Adda in the South Waziristan tribal region. The strike targeted fighters of Maulvi Nazir, a Pakistani militant commander who is accused of working with the Taliban and al-Qaida to direct cross-border attacks, the officials said, speaking on condition of anonymity as they were not authorized to talk to media on record.
Saturday's strike was the latest in a string of missile attacks targeting the militant-infested border region.
On Friday, U.S. missiles killed four unidentified people in a part of the North Waziristan tribal region where the Haqqani network holds sway. A day earlier, a strike in North Waziristan killed Janbaz Zadran, who U.S. officials say was a top commander in the Haqqani network and had helped orchestrate attacks in Kabul and southeastern Afghanistan.
The three attacks broke a relative lull in recent weeks, though that kind of tempo is not unusual.
So far this year, there have been more than 50 strikes, most of them North Waziristan region, where the Haqqanis are based. U.S. officials say the missiles are killing militants and their supporters; human rights groups have questioned that, saying civilian deaths are common.
Meanwhile, Pakistani police said Saturday they had arrested a Russian and two nationals from Azerbaijan in Lakki Marwat, a town located near North Waziristan. It was not clear how the men reached the region, which is off limits to foreigners, and authorities said they were still investigating to determine whether the men had any links to militant groups.