Pakistani Foreign Minister, Hina Rabbani Khar has complained to the US about the drone strikes
A US drone attack targeting a militant compound early on Saturday killed at least six insurgents in a troubled Pakistani tribal district along the Afghan border, security officials said.
The Pakistani officials said two missiles hit and destroyed the compound in Shawal area, some 70 kilometres (45 miles) west of Miranshah, the main town in North Waziristan.
Waziristan is the most notorious militant stronghold in Pakistan's semi-autonomous north-western tribal belt. Washington considers it the main hub for Taliban and Al-Qaeda to plot attacks on the West and in Afghanistan.
"A US drone fired two missiles at the compound. At least six militants have been killed. The death toll may rise," a security official in the north-western city of Peshawar told AFP.
Two security officials in Miranshah confirmed the strike and death toll and added that militants were using the compound as a training centre.
Pakistan and the United States are currently taking tentative steps to repair a serious crisis in relations over last year's covert American raid that killed Osama bin Laden and US air strikes that killed 24 Pakistani soldiers.
Pakistan says the drone strikes are counter productive and undermine government efforts to separate tribes from militants, violate Pakistan's sovereignty, kill civilians and fuel anti-US sentiment.
Saturday's attack was the second strike since Pakistan's parliament in March approved new guidelines on relations with the United States, which included a call for an end to drone attacks on Pakistani territory.
Pakistan raised the issue with Marc Grossman, the US special representative for Afghanistan and Pakistan, when he visited Islamabad last month amid efforts to mend fractured relations.
The frequency of the strikes has diminished in recent months, but US officials are believed to consider them too useful to stop them altogether.
US President Barack Obama in January confirmed for the first time that US drones target 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 New America Foundation think-tank in Washington says drone strikes have killed between 1,715 and 2,680 people in Pakistan in the past eight years.