SANAA, April 21 (Xinhua) -- The death toll of multiple U.S. drone strikes launched on Sunday against training camps of al- Qaida militants in Yemen's southern provinces of Abyan and Shabwa has risen to 55, the Yemeni Interior Ministry said on Monday.

Three local leaders were among the 55 dead militants, the ministry said in a brief statement on its website.

It said that its security services are working to identify the nationalities of foreign fighters who were killed among al-Qaida militants in the airstrikes.

The ministry described the air strikes as the strongest assault launched against the militants since 2012, when the army retook several cities of Abyan after months-long deadly battles with al- Qaida fighters.

In a reaction to the air raids, the militants assassinated Monday three senior intelligence officials in two separated attacks in central Sanaa, a day after four U.S. drone strikes killed the 55 suspected militants.

Security officials said the terrorist attacks were an angry reaction to the Sunday air raids on the militant hideouts in Abyan and Shabwa.

The Yemen-based al-Qaida offshoot has frequently staged revenge attacks on local targets, including military ones, and foreign missions in the impoverished Arab country.