ADEN (Reuters) - A blast in the southern Yemeni city of Aden killed four soldiers and wounded six, the city's security administration said, in an attack claimed by Islamic State.

The militant group said it had detonated an explosion among a group of soldiers in the port city, according to a statement posted to its online news agency Amaq.

One eyewitness told Reuters the bomb, which hit a checkpoint in the central Caltex area of the city, was planted in a plastic bag by a roadside.

Security officials and other witnesses said the blast was set off by a suicide bomber detonating an explosive vest.

Aden has been beset by attacks on troops claimed by Islamic State and Al Qaeda, and the two groups have gained strength as the government - backed by a military coalition led by Saudi Arabia - has fought against Yemen's dominant Houthi movement.

The civil war, which started in March 2015, has killed at least 6,400 people and caused a humanitarian crisis.

(Reporting By Mohammed Mukhashaf and Noah Browning; editing by John Stonestreet)