Aden (AFP) - Al-Qaeda overran a police headquarters in a south Yemen provincial capital on Saturday, strengthening their grip on the coast road overlooking the Gulf of Aden, security sources said.

The jihadists, who hold parts of the lawless south of the war-torn country, seized the headquarters in Zinjibar unopposed by pro-government forces who fled the capital of Abyan province, the sources told AFP.

The militants have controlled other government buildings in Zinjibar for weeks and also have a large presence in the nearby town of Jaar.

Earlier this week, they seized the town of Azzan in neighbouring Shabwa province.

They have also seized the towns of Shoqra and Ahwar, giving them complete control of the coast road between their stronghold city of Mukalla in the southeast and Zinjibar.

Zinjibar is only about 50 kilometres (30 miles) from Yemen's key southern city Aden, the government's temporary home after the capital Sanaa fell to Shiite rebels in September 2014.

The security sources also said that Al-Qaeda in the Arabian Peninsula (AQAP) has named Tawfiq Belaidi, brother of Jalal Belaidi who was killed in a suspected US drone strike on Thursday, as the "emir (ruler) of Zinjibar".

The US State Department said Jalal Belaidi was a regional AQAP emir responsible for multiple provinces in Yemen.

The United States had offered a $5-million reward for information on Belaidi over his alleged involvement in plotting bomb attacks on Western diplomatic officials and facilities in Sanaa in 2013.

Born in Abyan, the slain AQAP commander served in the past as Al-Qaeda chief in Zinjibar, but he is said to have climbed the ranks of the jihadist group to became a top military commander.

AQAP is seen by Washington as the extremist network's deadliest branch.

The US has kept up strikes on jihadists during months of fighting between pro-government forces and the Iran-backed Huthi rebels who control large parts of Yemen.

Loyalists backed by a Saudi-led coalition have recaptured Aden, Lahj, Abyan, Shabwa, and Daleh from the rebels since July.

But the Saudi-led coalition has so far not targeted jihadists including AQAP and the Islamic State group, who have gained ground in the south, attacking government officials and clashing with loyalist forces.