A US drone attack targeting a militant compound killed four insurgents in a troubled Pakistani tribal region early Thursday, security officials said.
In the second drone strike in about 24 hours, two missiles hit the compound located in Miranshah, the main town in volatile North Waziristan near the Afghan border, a security official said.
"A US drone fired two missiles at a compound used by militants in Miranshah and four militants have been killed," the official said.
The strike and death toll were confirmed by intelligence sources.
It followed a drone strike on Wednesday on a compound in Tappi, 10 kilometres (six miles) southeast of Miranshah, which security officials said killed 10 insurgents.
US officials say Pakistan's tribal belt provides sanctuary to Taliban fighting in Afghanistan, Al-Qaeda groups plotting attacks on the West, Pakistani Taliban who routinely bomb Pakistan and other foreign fighters.
But the missile attacks fuel widespread anti-American resentment, which is running especially high in Pakistan since US air strikes inadvertently killed 24 Pakistani soldiers in November.
President Barack Obama last month confirmed for the first time that US drones have targeted Taliban and Al-Qaeda militants on Pakistani soil, a programme that has escalated under his administration.
In a chat with web users on Google+ and YouTube, Obama said on January 31 that "a lot of these strikes have been in the FATA" - Pakistan's semi-autonomous Federally Administered Tribal Areas on the Afghan border.
According to an AFP tally, 45 US missile strikes were reported in Pakistan's tribal belt in 2009, 101 in 2010 and 64 in 2011.
The New America Foundation think-tank in Washington says drone strikes in Pakistan have killed between 1,715 and 2,680 people in the past eight years.
The United States had until now refused to discuss the strikes publicly, but the programme has dramatically increased as the Obama administration looks to withdraw all foreign combat troops from Afghanistan by the end of 2014.
US diplomatic cables leaked by WikiLeaks in late 2010 showed that Pakistan's civilian and military leaders privately supported US drone attacks, despite public condemnation in a country where the US alliance is hugely unpopular.
Islamabad is reviewing its entire alliance with the United States and has kept its Afghan border closed to NATO supply convoys since the November strike.
It ordered US personnel to leave Shamsi air base in southwestern Pakistan, widely believed to have been a hub for the CIA drone programme, and is thought likely to only reopen the Afghan border by exacting taxes on convoys.