An American drone strike in the frontier tribal areas of Pakistan killed 10 suspected militants Sunday, Pakistani officials said. It was sixth such strike in two weeks as the U.S. pushes ahead with its drone campaign in the face of Pakistani demands to stop.

The continued attacks emphasize the importance the U.S. government puts on the drone campaign, which it considers to be a vital tool in the war against Al Qaeda and the Taliban.

Two Pakistani intelligence officials say four missiles were fired at targets in the village of Mana Raghzai in South Waziristan near the border with Afghanistan on Sunday morning.

At the time of the attack, suspected militants were gathered to offer condolences to the brother of a militant commander killed during another American unmanned drone attack on Saturday. The brother was one of those who died in the Sunday morning strike. The Pakistani officials said two of the dead were foreigners, and the rest were Pakistani.

The American drone campaign has been a source of deep frustration and tension between the U.S. and Pakistan.

Under President Barack Obama, the U.S. stepped up its drone campaign in the border areas as a way to combat Al Qaeda and Taliban fighters who were using Pakistan as a base for attacks against American and NATO forces in Afghanistan. However, the number of drone attacks has eased in recent years.

Secretly, many Pakistani military commanders are believed to support the drone campaign. But among the Pakistani public, where the U.S. is viewed with mistrust, the drone strikes are considered an affront to the nation's sovereignty.

The Pakistani government and parliament have repeatedly asked the U.S. to stop the drone strikes.

The ongoing attacks are also complicating efforts for the U.S. and Pakistan to come to an agreement over reopening the supply routes to NATO and American forces in Afghanistan. American airstrikes inadvertently killed 24 Pakistani soldiers in November, prompting Islamabad to block U.S. and NATO supply lines running throught its territory.

Pakistan has demanded an apology over the raid and an end to drone strikes as a precursor to reopening the supply lines. But the U.S. has shown no intention of ending the attacks.

Also Sunday, gunmen killed four Shiite minority Muslims, a police officer and a bystander in a busy market of southwestern Pakistani city of Quetta, said police officer Abdul Wahid. He said police were investigating who could be behind the attack, but that it had a sectarian motive.

In the 1980s and 1990s, Pakistan became the scene of a proxy war between mostly Shiite Iran and Sunni Saudi Arabia, with both sides funneling money to sectarian groups that regularly targeted each other.

The level of sectarian violence has declined somewhat since then, but attacks continue. In recent years, Sunni attacks on Shiites have been far more common.