At least four people have been killed in a suspected US missile strike in northwest Pakistan, intelligence officials said.

The officials, who spoke on condition of anonymity, said on Saturday that the strike targeted suspected anti-government fighters in vehicles travelling in the Kurram tribal region.

The identity of those killed was not immediately clear.

"There were attacks in three different places on Friday evening," the Reuters news agency cited one government official in the region as saying.

The strike, like others in northwest Pakistan, was believed to have targeted the Haqqani Network,which is based in the area and considered by the US to be the greatest threat to Nato forces in eastern Afghanistan.

However, the US government does not acknowledge such missile strikes, which are reportedly run by the Central Intelligence Agency.

Pakistan is a US ally in the war against Taliban and al-Qaeda fighters, but it has voiced resentment over such pilotless drone aircraft attacks.

Islamabad considers remote-controlled attacks, which spark outrage among civilians in the country's tribal regions, a breach to its sovereignty.