Two separate US missile strikes killed at least 14 militants in northwest Pakistan Thursday, officials said, as Islamabad faces growing US pressure to dismantle Islamist extremist networks.

The attacks hours apart by unmanned US drone aircraft hit suspected militant hideouts in the same area of North Waziristan, part of the lawless tribal belt branded the most dangerous place in the world by Washington.

It was not clear which groups were targeted, with North Waziristan rife with Taliban militants, Al-Qaeda fighters and members of the Haqqani network, a powerful group known for staging attacks on foreign troops in Afghanistan.

In the deadliest attack, multiple drones launched an onslaught in the evening on several houses in North Waziristan's Ambarshaga area, about 30 kilometres (18 miles) west of the main district town Miranshah.

"Five US drones fired at least seven missiles, targeting two houses and two vehicles in the Ambarshaga area in North Waziristan and killing 12 militants," a senior security official in the area told AFP.

He said that those killed in the strike included at least four foreigners, adding that their nationalities could not be immediately established.

Pakistani officials mostly use the term "foreigners" to refer to Al-Qaeda recruits operating in the tribal regions.

He added it was also not clear whether any high-value target was present in the area at the time of attack.

Another security official confirmed the bombing by the drone and said the death toll may rise due to the intensity of the strike.

In a second attack in the same area, missiles fired by a US drone at around midday slammed into a house allegedly used by militants.

"The American drone fired two missiles, killing two militants and badly damaging a house and an attached guest portion. A car was completely destroyed," said a security official based in Miranshah.

"The militants rented out this house and were using it as a base."

A local intelligence official confirmed the strike and the death toll in the village of Dattakhel. Officials refused to be named because of the sensitivity of the US strikes in Pakistan, which inflame anti-American sentiment.

North Waziristan neighbours South Waziristan, where Pakistan has been focusing its most ambitious offensive yet against homegrown Taliban militants, sending about 30,000 troops into the region on October 17.

The military has launched multiple offensives this year against the Taliban and other militants across the semi-autonomous tribal belt, but so far North Waziristan has seen only limited airstrikes and no major ground offensive.

The region has, however, seen a rise in US strikes, which fan anti-Americanism in the nuclear-armed Muslim country, since US President Barack Obama took office and put the country on the frontline of the war on Al-Qaeda.

US media have reported that the White House authorised the CIA to expand the use of drones in Pakistan to strike suspected Taliban and Al-Qaeda members.

Since August 2008, at least 66 such strikes have killed around 628 people, although it is difficult to confirm the precise identity of those killed.

US officials said last week a senior Al-Qaeda figure was killed in a recent drone strike -- believed to be an attack reported on December 8 -- but security officials in Pakistan were unable to identify the body.

The Obama administration has been putting increased pressure on Islamabad not only to target the Pakistani Taliban staging attacks inside the country, but to stamp out militant groups who cross the porous border into Afghanistan.

Two senior US military officials visited Pakistan this week to discuss the battle against extremists and Obama's new strategy for the Afghan war.

Obama is deploying an extra 30,000 troops to try to turn the tide in the eight-year war against a Taliban-led insurgency in Afghanistan.

He has stressed that the plan hinges on Pakistan's own efforts against extremists, but the strategy has been criticised in Pakistan, where officials fear it may bring more militants fleeing over the border.