Authorities in Yemen's southern city of Aden imposed a curfew on Monday after violence blamed on suspected jihadists killed at least 17 people, pro-government media and security sources said.

Suspected Islamic State group jihadists also shot dead Sheikh Ali Othman, a Sufi imam who was considered a moderate, in the city, according to security officials.

The curfew will come into force at 8:00 pm (local time) and last until 5:00 am, the sabanews.net website said, citing a decision taken by the Aden Security Commission.

The decision comes after fierce battles on Sunday in the port of Aden that killed 17 people, among them nine members of the security forces including a colonel, the security sources said.

Security sources said the clashes erupted when forces loyal to President Abedrabbo Mansour Hadi met resistance as they tried to deploy in the port to secure it completely.

They said the fighting lasted several hours and that pro-Hadi forces eventually managed to take control of the port.

Witnesses said they saw an unprecedented number of armed men in Aden on Sunday, without being able to identify them.

Aden, declared by the government as Yemen's temporary capital, has been the scene of growing unrest as Al-Qaeda in the Arabian Peninsula, long active in Yemen, and IS appear to be vying for influence in the port city.

It was rocked by months of fighting last year between pro-government forces and Iran-backed Shia Houthi rebels who seized the capital Sanaa in September 2014 before expanding south.

Supported by a Saudi-led coalition, loyalists have regained control of Aden and four nearby provinces in the south since July as fierce battles persist across the country.