Six militants were killed in clashes with Yemeni government forces in the southern province of Abyan, a local official said on Monday, raising to 11 the number of Islamists killed in the area in two days.

Four people, including a soldier, were also wounded in the fighting in the provincial capital Zinjibar on Sunday night.

On Saturday, a local official said the army killed five suspected al Qaeda militants in Zinjibar, one of whom was Iraqi and another Saudi.

Abyan has been in a state of anarchy since militants, suspected of ties to al Qaeda, began seizing cities in the coastal region several months ago. The government said it had liberated Zinjibar from Islamist fighters in September.

Nine months of anti-government protests have paralysed impoverished Yemen, pushing it to the brink of civil war but failing to oust President Ali Abdullah Saleh.

Vice-President Abd-Rabbu Mansour Hadi, who has been mandated by Saleh to negotiate a power transfer deal under a Gulf-brokered plan to end the crisis, returned to Yemen on Monday after undergoing routine annual checks at a U.S. heart hospital, officials said.

Reports in opposition media said Hadi may have visited the United States to assuage pressure on Saleh to sign the Gulf power transfer plan which would see him stand down and trigger early presidential elections.

U.N. envoy Jamal Benomar, who visited Yemen in September in an unsuccessful bid to devise an operational mechanism for the Gulf initiative, is expected to return to Yemen on Thursday, an official at a U.N. office in Sanaa said.

Many say the standoff between the protesters and government forces has allowed militants to extend their control in Abyan.

In a speech on Saturday to mark the eve of the Muslim feast of Eid al-Adha, Saleh said he would leave office, after 33 years in charge, in line with a Gulf-brokered power transfer plan and lashed out at his deluded, malicious opponents.

(Reporting by Mohammed Mukhashaf in Aden and Mohammed Ghobari in Sanaa; Writing by Martina Fuchs and Firouz Sedarat; Editing by Philippa Fletcher)