Yemeni government forces entered Zinjibar on Sunday backed by Saudi-led air strikes as they launched an offensive to recapture southern Abyan province and its capital from Al-Qaeda militants.

Government forces backed by the Arab coalition began an all-out offensive in March against militants in south Yemen, recapturing main cities they had held.

But they later retreated from Zinjibar after Al-Qaeda militants struck back.

On Sunday they re-entered the provincial capital of Abyan after clashes with Al-Qaeda militants who have exploited a power vacuum in Yemen to expand their presence in the country's south and southeast.

"Zinjibar was retaken from Al-Qaeda fighters, most of whom have fled" the city, said military commander Abdullah al-Fadhli who is leading the offensive.

He said fighting was still underway however in northern districts of the city where militants were still holed up.

Yemeni authorities have trained hundreds of soldiers in the nearby province of Aden over the past two months to retake Abyan and they began to arrive in the southern province on Saturday, officials said.

Their advance had been slowed down in past attempts by mines and explosive devices planted by the militants on the road linking Abyan province with Aden, where the government is now based.

Saudi-led coalition warplanes have provided air cover to the pro-government forces pounding Al-Qaeda positions across Abyan, army sources said.

Late Saturday four militants were killed in strikes that targeted the coastal town of Shoqra.

Government forces meanwhile fired artillery rounds at Zinjibar and the nearby town of Jaar, a key Al-Qaeda stronghold, ahead of entering the provincial capital, the military source said.

Also on Sunday, a suicide bomber rammed his vehicle into a military convoy killing three soldiers in Abyan, army sources said.

Al-Qaeda has exploited turmoil in Yemen, where the government is battling Iran-backed Houthi rebels, to expand its influence in the country.

The Arab coalition which backs the Yemeni government against the Houthis has turned its sights on the militants, and the United States has pressed its drone war against them.

Washington considers the Yemen-based Al-Qaeda in the Arabian Peninsula, or AQAP, to be the extremist network's deadliest franchise.