Two US drone strikes struck Islamist militants in Pakistan's tribal badlands on Thursday, killing at least 13 fighters in North Waziristan near the Afghan border, officials said.
The aircraft fired missiles hours apart on separate targets in what is considered the premier bastion of Taliban and al Qaeda in Pakistan as the government in Islamabad welcomed the Afghan and Iranian leaders for a summit.
Five militants were killed in the first attack that destroyed a compound in Spalga town near Miranshah and at least eight died in the second attack on a vehicle near the town of Mir Ali, about 25 kilometres (16 miles) to the east.
"The death toll may rise," a Pakistani security official warned AFP after the second strike targeted militants travelling in a double cabin pick-up.
"At least eight militant have been killed in the second strike," he said, describing them all as "foreigners".
Another security official in Miranshah, the capital of North Waziristan, put the death toll at 12, saying they were all Uzbek Islamist fighters.
"The vehicle caught fire and the dead bodies are badly mutilated," he added.
The United States says Pakistan's tribal belt provides sanctuary to Taliban fighting in Afghanistan, al Qaeda groups plotting attacks on the West, and Pakistani Taliban who routinely bomb Pakistan and other foreign fighters.
Those killed in the first attack were loyalists of Badar Mansoor and the Haqqani network, loyal to the Afghan Taliban whose leaders are understood to be based in North Waziristan, one of the Pakistani officials said.
Last Thursday, officials said Mansoor, described as the "de facto leader of al Qaeda in Pakistan" was killed in a drone strike in North Waziristan.
Mansoor was considered one of America's main targets in the country, wanted for bomb attacks on the minority Ahmadi sect that killed nearly 100 people in May 2010 and the chief link between al Qaeda and the Pakistani Taliban.
The United States has blamed the Haqqani network for some of the most spectacular attacks carried out in Kabul, including last September's siege of the US embassy.
On Thursday, Pakistan hosted Afghan President Hamid Karzai and Iranian leader Mahmoud Ahmadinejad for a regional summit at a key juncture in peace efforts with the Taliban.
President Barack Obama last month confirmed for the first time that US drones target Taliban and al Qaeda militants on Pakistani soil, but American officials do not discuss details of the covert programme.
According to an AFP tally, 45 US missile strikes were reported in Pakistan's tribal belt in 2009, the year Obama took office, 101 in 2010 and 64 in 2011.
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.
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.
Pakistan 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 the 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.