Three suicide bombings claimed by the DAESH terrorist organization on Friday struck checkpoints of Yemeni government forces in Aden, killing at least 22 people, including 10 civilians, a security official said.
The bombings were followed by an attempt to attack a nearby large base of the Saudi-led Arab pro-government coalition which recently turned its guns on militants in southern Yemen.
The attacks came a year after the coalition launched on March 26, 2015 an air campaign against Shiite Houthi militants in support of internationally backed President Abd Rabbuh Mansour Hadi.
Two bombs went off simultaneously at separate checkpoints in Shaab district, on Aden's western outskirts, before gunmen launched an attack on the nearby base of the military coalition, an official said.
Apache helicopters belonging to the coalition carried out strikes on positions of gunmen in the surrounding area as the assailants tried to advance toward the base.
A third explosive device planted in an ambulance was detonated at checkpoint near Mansura, in central Aden, the official said.
The DAESH and Al Qaeda have exploited the chaos, widening their footholds in the south and carrying out deadly attacks, mostly against forces loyal to Hadi.
A US air strike on Tuesday on an Al Qaeda training camp in the southeastern province of Hadramawt killed more than 70 militants in a major blow to the group.
Al Qaeda's branch in Yemen is considered by Washington to be the most dangerous affiliate of the international terror organisation.
The Arab coalition launched its air campaign against the Houthis in March last year as the Iran-backed militants advanced on Hadi's refuge in Aden and forced him to flee to Riyadh.
Government forces have since managed to drive the Houthis out of Aden and four other southern provinces, thanks to the military support of the coalition.
But the coalition has failed to deal a decisive blow to the Houthis and their allies, who continue to control large parts of Yemen, including the capital Sanaa, which they seized in September 2014.
The United Nations says about 6,300 people have been killed since March last year, with civilians accounting for more than half.
New hopes for a breakthrough in the conflict surfaced on Wednesday when UN envoy Ismail Ould Cheikh Ahmed said warring parties had agreed on a ceasefire that would be observed before peace talks start on April 18.
Previous negotiations have failed and several ceasefires were never respected.