Two Yemeni army colonels, five soldiers and seven Islamist militants died overnight in fighting in southern Yemen, while artillery and air raids killed 15 pro-government tribesmen by mistake, local and tribal officials said on Saturday.

The clashes flared outside Zinjibar at the center of the Abyan province, where militants have seized several areas, a local official told Reuters. The region abuts an international shipping lane where three million barrels of oil pass daily.

A colonel and five soldiers were killed in an ambush and seven militants died in clashes that followed. Another colonel was killed in a separate shootout, the local official said.

A tribal official said the army and air force targeted the tribesmen after mistaking them for militants as they approached Zinjibar in another location late on Friday, killing 15 of them.

The militants' increasing threat to army control in south Yemen is kindling fear in the West and neighboring Saudi Arabia that al Qaeda's Yemen wing is taking advantage of political turmoil and six months of anti-government protests.

The Yemen-based al Qaeda in the Arabian Peninsula (AQAP), released an audio recording by its military commander on an Islamist website on Friday, in which he vowed to attack Saudi Arabia, the world's top oil exporter.

Opposition leaders have accused President Ali Abdullah Saleh of deliberately allowing Zinjibar and the other areas to fall to al Qaeda-linked militants for the time being in an effort to show how chaotic Yemen would be without him.

On Friday, tens of thousands gathered for protests both for and against President Saleh's three-decade rule.