At least four people, suspected to be Islamist militants were killed on Monday when missiles from a US drone aircraft struck a suspected insurgent hideout in Pakistan's northwest tribal belt, officials said.
It was the second such strike in 48 hours.
Three missiles struck a compound mid-morning in the Khushali Toorkhel area, about 25 kilometres east of Miranshah, North Waziristan's main town.
"The target was a militant compound belonging to followers of a local rebel commander Haleem Khan, and the US drone fired three missiles," a senior Pakistani security official said, asking not to be named.
"Four militants were killed while several others were wounded in the strike. The death toll may rise," he added.
Another security official confirmed the strike and the toll, but said the nationalities and identities of the dead were not yet known.
Officials said that Khan had ties to Taliban-linked warlord Hafiz Gul Bahadur, who is reputed to control up to 2,000 fighters in the region who stage attacks over the border against foreign forces stationed in Afghanistan.
The US has been pummeling North Waziristan with drone strikes this year, the last one on Saturday killing seven militants in the district.
More than 880 people have been killed in nearly 100 drone strikes in Pakistan since August 2008, and the bombing raids fuel anti-American sentiment in Pakistan and draw public condemnation from the government.
But officials in Washington say the strikes are a vital tool to protect the approximately 126,000 foreign troops in Afghanistan, and have killed a number of high-value targets including Pakistani Taliban chief Baitullah Mehsud.
Many officials also believe his successor Hakimullah Mehsud was killed in a strike in January, but there has been no official confirmation of his death.
Under US pressure, Pakistan has in the past year significantly increased operations against militants in the area, which Washington has called the most dangerous region on Earth and a global headquarters of Al-Qaeda.
Pakistan last year launched its most ambitious military offensive yet against Taliban militants in South Waziristan, expanding the campaign to many of the other seven semi-autonomous tribal districts hugging the Afghan border.
The military has, however, appeared reluctant to launch a similar all-out assault into North Waziristan, where many insurgents have sought sanctuary.