A U.S. drone strike targeting a militant hideout in northwest Pakistan killed at least 10 militants Sunday.

Intelligence officials said the drone fired four missiles into the compound in South Waziristan tribal region bordering Afghanistan. They said the missiles hit a group of people that had gathered to offer condolences to the brother of another militant killed in a drone strike a day earlier.

It was the sixth U.S. drone strike in two weeks, despite Pakistani demands to stop them. Islamabad says the missile attacks are counter-productive, violate the country's sovereignty, kill civilians and fuel anti-U.S. sentiment.

However, Washington considers them to be a vital tool in the war against al-Qaida and the Taliban.

The drone strategy has become an increasingly contentious issue between the two sides, following a November strike that mistakenly killed 24 Pakistani soldiers stationed near the Afghan border.

Pakistan's parliament has demanded an apology for the cross-border attack and an end to drone strikes on Pakistani soil, but Washington has refused, prompting Islamabad to block U.S. and NATO supply routes into Afghanistan. Islamabad has not yet reopened the routes, further straining already tense relations between the two sides.

Pakistani security analyst and retired Lieutenant-General Talat Masood says opposition parties in the country are exploiting the situation which, he says, “is politically becoming very much untenable.”

Another analyst, Rustam Shah Mohmand says that although the political and military establishments seem to be playing down the attacks, the long term implications could create more resentment and hostility towards the U.S. from the Pakistani people.