SANAA, Yemen — Two suspected al-Qaida militants were killed on Monday in a drone strike on their vehicle south of the capital Sanaa, tribal and government sources said.

The strike follows another on Saturday in which at least four militants were killed in Abyan governorate, in southern Yemen. A Yemeni official did not say who was behind the attack, but previous strikes have been carried out by the United States.

Monday's strike occurred at dawn in the Radda area in al-Bayda province, but the sources gave no further details and Washington does not usually comment on drone strikes.

The United States has stepped up attacks on Yemen-based al-Qaida in the Arabian Peninsula (AQAP), once described by a senior U.S. official as the group's most dangerous branch after a plot by it to attack international airliners was foiled.

Yemen is next to the world's top oil exporter Saudi Arabia and major crude shipment routes.

Yemeni officials have said that at least six suspected militants were killed in two drone strikes last month. Another six suspected al-Qaida members were killed in January.

Militants allied to AQAP exploited Arab Spring chaos in Yemen in early 2011 to seize control of some towns in the country's southern provinces, including Radda and Jaar, where Saturday's strike occurred.

Although they were pushed from the towns last year they continue to fight government forces.