At least 18 people were killed in three ISIS-organized synchronized bomb attacks on Yemeni government forces in the southern port city of Mukalla on Monday, medics and security sources said.

Scores of other people were wounded in the bombings, which occurred just as soldiers were about to break their day-long fast during the Muslim holy month of Ramadan.

The terrorist group ISIS claimed responsibility for the attack via their online news agency. The first explosion hit as an attacker detonated his suicide vest at a checkpoint on Mukalla’s western entryways.

A second blast came from a bomb-laden car at the military intelligence headquarters, and the last was an improvised explosive device which went off as soldiers were about to begin their evening meal.

Mukalla, capital of the vast eastern province of Hadramout and an important shipping center, was the former stronghold of a wealthy mini-state that Al Qaeda in the Arabian Peninsula (AQAP) built up over the past year as it took control of an almost 600-km band of Arabian Sea coastline.

In late April, Yemeni and Emirati soldiers regained control over Mukalla from AQAP, which put up little resistance before withdrawing its forces.

Terrorists in Yemen had also carried out a suicide bombing in the southern port city of Aden on May 23 which killed 40 army recruits, the latest in a string of attacks claimed by the group.

Extremist militants have gained territory and freedom to operate thanks to a war raging for over a year in which government forces have been pitted against Iran-allied Houthi rebels who control the capital Sanaa.

In an initial reading of the attacks, Yemeni security officials believe there is an overlap between militants supporting Al Qaeda and ISIS, though the two groups are ideological rivals and compete for recruits.

“Sleeper cells still exist in Mukalla and we are working against them every day,” a security official said.

“Since the liberation of the city, security forces have arrested hundreds of Al Qaeda fighters in raids, uncovered plots and seized around 20 explosive cars.”