Government forces have clashed with fighters for control over the strategic southern port of Aden, Yemeni officials in the southern city say.
The officials said on Sunday that fighters believed to be close to al-Qaeda have refused to hand over the port to the government of President Abd-Rabbu Mansour Hadi.
At least one armed group is reportedly using the port to run lucrative smuggling operations.
On Thursday, a drive-by shooting in Aden killed Ahmed al-Idrisi, a senior leader of a pro-government group, just hours after he reluctantly agreed to hand over control of the port to government troops.
Security officials said Idrisi publicly backed the government, but maintained secret deals with armed groups and anti-government forces.
All officials spoke on condition of anonymity because they were not authorised to speak to reporters.
A loose alliance of Yemeni loyalists, backed by a coalition of mostly Arab countries assembled by Saudi Arabia, reclaimed control of Aden in July.
The Arab coalition launched an offensive against Yemen's Iran-allied Shia Houthi forces and their allies in March, when Hadi first fled Aden to the Saudi capital, Riyadh.
Although the war began with air strikes, the coalition went on to provide ground forces in the war.
Pro-government forces have set up a blockade of the capital, Sanaa, as Arab coalition forces continue to launch strikes against the Houthis and their allies.
Speaking to Al Jazeera from Riyadh on Sunday, Brigadier-General Ahmed Asiri, spokesman for the coalition, defended the resumption of air strikes.
He took issue with a UN report in December saying that more than 100 tonnes of aid was delivered to Taiz.
"The humanitarian organisation belonging to the UN signed an agreement and they took the money and sent the shipment," he said.
"But they did not get on the ground to distribute the aid, so it got to the Houthis and they used it to humiliate the people. So why did the UN not condemn this action which prevented people from obtaining food and medicine?"
Source: Al Jazeera and agencies