* Yemen is home to one of most active al Qaeda wings
* Four attacks on militants in four days
* Discontent over drone attacks growing
SANAA, Jan 22 (Reuters) - A U.S. drone killed four suspected al Qaeda militants on Tuesday in a strike on their car in northern Yemen as they drove away from a militant training ground, according to tribal sources and local officals, the fourth such attack in four days.
The United States never comments on strikes by its pilotless aircraft, which it has used to track down militants in Yemen for years. The Yemeni government tolerates such strikes but usually does not comment on the U.S. role in specific incidents.
Washington has scaled up action against al Qaeda in Yemen, where the group exploited widespread anti-government unrest in 2011 to seize swathes of territory in the south.
It was subsequently driven out by a military offensive in June last year.
The four men were travelling in a vehicle through the desert in the Yemeni province of al-Jawf, near the border with Saudi Arabia, a tribal source told Reuters, declining to be named.
"The strike targeted a gathering of al Qaeda members who had made the area a centre for training. One of the cars was hit and everyone inside was killed ... the others fled," a local official told Reuters, also declining to be identified.
Shoring up stability and security in Yemen is a priority for the United States and its Gulf Arab allies because of its location next to the world's top oil exporter, Saudi Arabia, and to shipping lanes, and because it is home to one of the most active wings of al Qaeda.
Al Qaeda in the Arabian Peninsula (AQAP) is considered by Western governments to be one of the most dangerous arms of the global network founded by Osama bin Laden, and has attempted a number of attacks against U.S. targets.
Another four suspected insurgents were killed in a strike in central Yemen on Monday, while six more were killed in drone strikes in Maarib on Saturday and Sunday. A further 10 suspected al Qaeda fighters died in an explosion in a house in southern Yemen on Sunday.
But discontent at the drone strikes is growing. Earlier on Tuesday, a Yemeni cabinet minister criticised drones and urged a move to ground operations to avoid hurting civilians.
On Sunday armed tribesman, angry at what they said was a drone attack on an area inhabited by civilians, blocked the main road linking Maarib with Sanaa.
Earlier this month, dozens of armed tribesmen also took to the streets in southern Yemen to protest against drone strikes that they said had killed innocent civilians and fuelled anger against the United States. (Reporting by Mohammed Ghobari; Writing by Raissa Kasolowsky; Editing by Alison Williams)