In the internationally recognised government's temporary capital of Aden, fighting broke out in the Mansura residential district after security forces set up new checkpoints, they said.
Dozens of gunmen in balaclavas carrying the Al-Qaeda flag deployed to push back police trying to enter the neighbourhood, witnesses said.
Late today, jihadists shot at an Apache helicopter from the Saudi-led military coalition backing the police, they said, before a fighter jet intervened to strike jihadist positions.
Meanwhile, pro-government forces on today pressed their offensive aimed at breaking the rebels' months-long siege of the southwestern city of Taez, military sources said.
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Fighting raged north and east of the city, they said, a day after loyalists pushed the Iran-backed Huthis out of its western and southern suburbs.
Forces loyal to President Abedrabbo Mansour Hadi managed to "retake important positions" in a northern suburb where heavy clashes continued, one source said.
The rebels and their allies have been attacking residential neighbourhoods of Taez from this area, which includes an airport, an industrial zone and the headquarters of the special forces, the source added, without giving a death toll for the fighting.
Loyalists today morning pushed back rebels trying to retake the headquarters of the army's 35th brigade in the western suburbs, sources said.
Loyalists last summer retook five southern provinces including Aden and have for months been fighting to win back Taez.
The capital Sanaa further north has been under rebel control since September 2014.