Rebel Coup Ousts Yemen's Leader

Fighting was earlier reported around the presidential palace in the capital, Sanaa, a day after heavy fighting between government forces and Houthis Shiite Muslims who have long felt marginalized in the majority Sunni Muslim country ended in a ceasefire deal.

Nine people were killed and 67 others injured on Monday, Yemen's Health Ministry said, before the sides agreed to a ceasefire.

Gunfire could be heard sporadically across the city Tuesday, whereas a day earlier it was constant.

Unknown assailants fired shots Monday night at a U.S. Embassy vehicle in Sanaa, the U.S. Embassy said Tuesday.

Yemen's presidential palace has been completely taken over by Shiite Houthi rebels, the country's Minister of Information Nadia Sakkaf told CNN on Tuesday amid reports of renewed clashes.

Sakkaf said the Prime Minister's residence was also under attack from the street.

She called the situation "the completion of a coup," adding that "the President has no control."

Prolonged turmoil

The latest violence comes at a time of prolonged turmoil and intermittent clashes between government and opposition forces in Yemen, a U.S. ally in the battle against al Qaeda.

The government faces pressure from not only the Sunni Muslim extremist group al Qaeda in the Arabian Peninsula but also Houthi militants.

Houthis swept into the capital last year, sparking battles that left more than 300 dead in a month. In September, they signed a ceasefire deal with the government, and Houthis have since installed themselves in key positions in the government and financial institutions.

But tensions flared again last weekend as Houthis said they abducted presidential Chief of Staff Ahmed bin Mubarak in Sanaa on Saturday. Osama Sari, senior media adviser to the Houthi movement in Yemen, said Houthis detained bin Mubarak because President Abdu Rabu Mansour Hadi wanted to introduce a new constitution without the Houthis' approval.

Turmoil between the two sides is worrisome to the West because a power vacuum in Yemen could benefit al Qaeda in the Arabian Peninsula, a terrorist organization based in Yemen that took credit for the attack on the offices of Charlie Hebdo in Paris. It also tried to blow up a plane landing in Detroit in 2009.

U.N. chief 'gravely concerned'

U.N. Secretary-General Ban Ki-moon's spokesman said Ban was "gravely concerned about the deteriorating situation" in Yemen.

"The secretary-general calls on all sides to immediately cease all hostilities, exercise maximum restraint, and take the necessary steps to restore full authority to the legitimate government institutions," the spokesman said.

"All sides must abide by their stated commitments to resolve differences through peaceful means."

Ban also condemned the kidnapping of bin Mubarak and called for his immediate release.

Mark Lyall Grant, UK ambassador to the United Nations, said the U.N. special adviser on Yemen, Jamal Benomar, was on his way to Sanaa and would brief the U.N. Security Council from there.

"There's a lot of conflicting reports, but clearly the situation has deteriorated very significantly over the last 48 hours, and that's why the Security Council needs to meet and decide its response," the UK envoy said.