Triple bomb attacks claimed by the Islamic State (IS) group have killed at least 35 people and injured 24 in Yemen's south-eastern city of Mukalla, according to BBC News.

The militants struck at sunset as soldiers were preparing to break their day-long fast during the Muslim holy month of Ramadan, officials say.

The attacks involved a suicide bomber, a car bomb and an improvised explosive device, Reuters news agency reports.

An offshoot of al-Qaeda controlled the port city until recently. It was recaptured in April by Yemeni government and Saudi-led coalition forces.

The first explosion occurred as an attacker detonated his suicide vest at a checkpoint on Mukalla's western approaches, Reuters says.

A bomb-laden car then exploded at the military intelligence headquarters, while the last bomb went off as soldiers were preparing to eat, the agency says.

The al-Qaeda in the Arabian Peninsula (AQAP) group had taken advantage of Yemen's civil war to seize territory, weapons and money.

Yemeni security officials believe there is an overlap between AQAP loyalists and IS, despite the rivalry between the two groups, Reuters says.

"Sleeper cells still exist in Mukalla and we are working against them every day," a security official was quoted as saying.

"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."

Pro-government and coalition forces had previously focused on battling Houthi rebels and military units loyal to former President Ali Abdullah Saleh.

More than 6,400 people, half of them civilians, have been killed in Yemen's conflict, while almost 2.8 million others have been displaced, according to the UN.