By Mohammed Mukhashaf

ADEN (Reuters) - Forces loyal to Yemen's president said they had seized strategic buildings in the southern city of Aden on Monday after a five-hour battle, escalating a civil conflict threatening to split the country in two.

The militias supporting Abd-Rabbu Mansour Hadi wrested parts of Yemen's economic hub from security forces allied to the Houthi movement, including its main power station and intelligence headquarters, sources said.

The country's north is dominated by the Shi'ite Muslim Houthis, who completed a takeover of the capital Sanaa last month. In the south, forces loyal to Hadi and separatists aiming to restore the former South Yemen appear to be in charge.

U.N. Yemen envoy Jamal Benomar tweeted on Monday that he had visited Hadi, who is still under house arrest at his residence.

Benomar said he had briefed Hadi on the U.N. Security Council resolution adopted on Sunday calling for an end to his house arrest and that of his government.

The United Nations Security Council on Sunday urged the Houthis to quit government institutions, threatening further steps if the violence does not stop.

Minister of Information Nadia al-Sakkaf tweeter that she had also visited Hadi on Monday, adding he had a heart condition and was "quite ill".

The Houthis forced Hadi to resign during their takeover, but he remains de jure president. They tried to dissolve the assembly two weeks ago, but its largest group, the General People's Congress party (GPC), objected.

The GPC said on Monday it had withdrawn its objection, boosting chances of a consensus in multi-party talks on picking a new national administration.

Violence has escalated recently, filling the political vacuum left in January when the Houthis seized the presidential palace and forced Prime Minister Khaled Bahah's government to resign.

Tens of thousands of Yemenis demonstrated in several cities on Saturday against Houthi rule as clashes between Houthis and Sunnis in a southern region left 26 dead.

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In clashes overnight, sources in the Popular Committees of Aden, run by Hadi's brother, Nasser, said they had also taken Aden's television station and the administrative building of its free trade zone, with the loss of three fighters.

The Popular Committees confirmed several government buildings had been taken. Aden's governor, Abdel-Aziz bin Habtour, confirmed the clashes but denied Hadi loyalists had taken over the television station.

"The situation is under control and what has happened is being dealt with," a Defense Ministry website quoted him as saying.

Turkey becoming the latest country to withdraw its diplomats from Sanaa on Monday, following the closure of the embassies of the United States, major European nations and Saudi Arabia in recent weeks.

(Additional reporting by Mohammed Ghobari in Sanaa, writing by Maha El Dahan, editing by Sami Aboudi and Tom Heneghan)