Sanaa: Yemen`s second city Aden shut its airport in support of President Abdrabuh Mansur Hadi on Wednesday amid growing international concern over attacks by Shiite militia on the authorities.
The powerful militia, known as Huthis, seized almost full control of the capital Sanaa in September and have fought pitched battles with government forces this week as they press for more political power.
At least 18 people have been killed in the fighting that erupted on Monday and dozens more wounded, medical sources said.
On Tuesday, the militia seized Hadi`s offices at the presidential palace and attacked his residence, in what officials said was an attempt to overthrow the government.
The UN Security Council condemned the attacks and backed Hadi as Yemen`s "legitimate authority".
Gulf foreign ministers were due to hold an emergency meeting in Riyadh Wednesday to discuss the crisis.
The six-member Gulf Cooperation Council (GCC) has previously demanded the Huthis withdraw from Sanaa and other parts of the country they seized after sweeping south from their stronghold in Yemen`s rugged north.
Aden`s main security body said in a statement that it was closing its airport, its seaport and entrances to the city due to "dangerous developments in the capital" and "attacks on the symbol of national sovereignty and constitutional legitimacy."
Aden is the main city in southern Yemen, which was an independent country from 1967 to 1990 and where a separatist movement still exists.
Residents said hundreds of pro-government militia fighters had also arrived in Aden from several southern provinces.
The rising unrest has fuelled longtime divisions in Yemen, where the government, Huthis, southern separatists, powerful Sunni tribes and the local Al-Qaeda branch are all vying for influence.
It has raised fears of a collapse of Hadi`s Western-backed government, a key ally in Washington`s fight against Al-Qaeda, and the country descending into chaos.The Huthis began increasing pressure on the authorities on Saturday with the kidnapping of Hadi`s chief of staff, Ahmed Awad bin Mubarak, in an apparent bid to extract changes to a draft constitution opposed by the militia.
Mubarak is leading efforts to reform how the country is governed under a "national dialogue" set up after former strongman Ali Abdullah Saleh was forced from power in February 2012 following a year of bloody protests inspired by the Arab Spring.
His plans for dividing Yemen into a six-region federation have angered the Huthis, who claim it would split the country into rich and poor regions.
Both Hadi and Mubarak are from the south.
Heavy fighting broke out on Monday around the presidential palace and in other parts of Sanaa, with the Huthis seizing a key army base, taking control of state media and firing on a convoy carrying the prime minister, before a ceasefire was agreed.
Clashes resumed late on Tuesday, with the militiamen seizing the palace and looting its arms depots and attacking Hadi`s residence elsewhere in the capital.
In a long televised speech after fighting subsided, defiant militia leader Abdul Malik al-Huthi warned that "all options" were open against Hadi, whom he accused of supporting the "fragmentation" of the country.
Residents said the capital was tense but calm on Wednesday.
At an emergency meeting late Tuesday, the UN Security Council called for a full ceasefire and a return to dialogue, but did not threaten further action.
In November it slapped sanctions on two of the militia`s commanders, though not on Huthi himself, and on Saleh, who has been accused of backing the militia.
Since they seized Sanaa, the Huthis have pressed their advance south of the capital, where they have met stiff resistance from Sunnis, including Al-Qaeda loyalists.
Yemen`s branch of the jihadist network, Al-Qaeda in the Arabian Peninsula, is considered the militant group`s most dangerous and claimed responsibility for this month`s deadly attack on French satirical weekly Charlie Hebdo.
Hadi`s government has allowed Washington to carry out repeated drone attacks on Al-Qaeda militants in its territory.