Yemen's prime minister yesterday accused southern separatists of an attempted coup after they took over the government headquarters amid fierce clashes in the city of Aden.

Prime Minister Ahmed bin Dagher called on the Saudi-led military coalition, which has been backing the government against Shia Huthi rebels in control of much of the north, to intervene in its defence.

Security sources and residents said fighting appeared to have spread to most of the southern port city of Aden, throwing Yemen into further chaos after years of civil war.

The southern separatists -- who want the return of an independent state that ended with Yemen's unification in 1990 -- had backed President Abedrabbo Mansour Hadi's government against the Huthis but tensions between the two sides had been on the rise.

"A coup is ongoing here in Aden against legitimacy and the country's unity," Dagher said in a statement.

Security sources told AFP that pro-separatist units trained and backed by the United Arab Emirates had taken over the government headquarters in Aden after clashes.

At least 15 people were killed and dozens wounded, hospital sources said. President Hadi yesterday ordered his forces to cease fire immediately in Aden.

The fighting erupted after separatist protestors were prevented from entering the city for a protest to demand the government's ouster from Aden, established as its interim base after the Iran-backed Huthis seized control of the capital Sanaa in 2014.

The coalition, which launched its intervention against the rebels in March 2015, had urged restraint ahead of the planned protest.

Universities, schools and the only international airport in the city had all been closed, according to witnesses.

Dagher said that events in Aden were headed towards "total military confrontation" and urged members of the coalition, in particular the UAE, to take action.

The premier also warned that separating south Yemen from the rest of the country would benefit Iran and the Huthis.

"Iran is trying to consolidate its presence in Yemen through the Huthis and by splitting Yemen, we are giving them one-third of the land and three-quarters of the population," Dagher said.