A US air strike last month killed four suspected Al-Qaeda militants in Yemen, the ninth such attack this year, the US military disclosed on Friday.

The strike on May 19 took place in the southern province of Shabwa, US Central Command (Centcom) said in a statement.

It brought to nine the number of US air strikes against Al-Qaeda in the Arabian Peninsula (AQAP) since the beginning of the year, the statement said.

Four of the strikes had not previously been disclosed.

US attacks have killed a total of 81 suspected AQAP fighters, the statement said.

An air strike against a training camp on March 22 killed 56 militants, according to Centcom's latest tally.

The United States, which has considered AQAP the most dangerous Al-Qaeda branch since 2009, regularly conducts airstrikes against the jihadist group in Yemen, mostly using drones.

AQAP has taken advantage of the country's civil conflict between Houthi rebels and Yemeni government forces to expand its influence in the country's south and southeast.

US soldiers had been deployed in Yemen until March 2015, when the last troops left the country in the face of a Houthi rebel advance.

However, a "very small number" of US soldiers recently returned to the southern port of Mukalla, retaken from AQAP in April, the Pentagon confirmed last month.

The soldiers were deployed to support Yemeni forces and the Arab coalition taking part in the fight against Al-Qaeda in the region.

AQAP is "using the unrest in Yemen to provide a haven from which to plan future attacks against our allies as well as the US and its interests," Centcom's statement said.

"The United States will not relent in its mission to degrade, disrupt and destroy Al-Qaeda and its remnants."