Houthi Shiite Yemenis check a car as they guard a street during clashes near the presidential palace in Sanaa, Yemen, Monday, Jan. 19, 2015. Rebel Shiite Houthis battled soldiers near Yemen's presidential palace and elsewhere across the capital Monday, despite a claim of a cease-fire being reached to halt the violence, witnesses and officials said. (AP Photo/Hani Mohammed)

SANAA, Yemen - Yemen's U.S.-backed leadership came under serious threat Monday as government troops clashed with Shiite rebels near the presidential palace and a key military base in what one official called "a step toward a coup."

The militants seized control of state media in fierce fighting that marked the biggest challenge yet to President Abed Rabbo Mansour Hadi by the rebels, known as Houthis, who swept down from their northern strongholds last year and captured the capital in September.

The violence threatened to undermine efforts by the U.S. and its allies to battle al-Qaida's Yemeni affiliate, which claimed responsibility for the attack on a Paris satirical magazine this month and which Washington has long viewed as the global network's most dangerous branch.

The Houthis and forces loyal to Hadi have been in a tense standoff for months and the two sides traded blame for the outbreak of violence Monday. Witnesses said heavy machine-gun fire could be heard as artillery shells struck around the presidential palace. Civilians in the area fled as columns of black smoke rose over the palace and sirens wailed throughout the city.

Hadi, whose government has ceded control over nearly the entire capital, doesn't live at the palace, and extra soldiers and tanks deployed around his private residence, which is nearby.

As fighting escalated Monday, the convoys of Yemen's prime minister and a top official affiliated with the Houthis came under fire, and rebel fighters took over Yemen state television and its official SABA news agency, Information Minister Nadia Sakkaf said.

"This is a step toward a coup and it is targeting the state's legitimacy," Sakkaf told The Associated Press.

Cease-fire negotiations continued throughout the day by a presidential committee that included the interior and defence ministers, a presidential aide and a tribal sheik close to the Houthis. By the end of the day, a tenuous truce appeared to be holding.

The announcement of a cease-fire came after witnesses said the rebels had seized control of strategic hills that overlook both the palace and the military camp south of it. There was no government confirmation of the loss of territory.

At least nine people were killed in the fighting and 67 were injured, Yemen's deputy health minister, Nasser Baoum, told the AP.

Yemen's Western and international allies, including the U.S and Saudi Arabia, called for steps to implement and consolidate the cease-fire, expressing their support for Hadi.

"We reject the use of violence by those who seek to overturn Yemen's political transition for their own interests, and fully support President Hadi as the legitimately-mandated president," a statement on the U.S. Embassy website said.

The Houthis blamed Hadi for the escalation in hostilities, saying he reneged on a U.N.-sponsored agreement with the group in September that promised better representation on a committee to oversee the drafting of a new constitution. According to the agreement, Hadi was to appoint new members within 15 days to the 85-member national committee.

Hisham Al-Omeisy, a Yemeni activist who lives near the presidential palace, said the fighting began just after 6 a.m., with a shell hitting a hill controlled by the Houthis. The militants responded with heavy artillery fire, he said.

Al-Omeisy said he saw two bodies in civilian clothes just outside his house, but couldn't tell if the dead were civilians or Houthis, who do not wear uniforms.

"Later, I thought it was all quiet and I left my house. But a shell landed right near me," he told the AP.

Khaled al-Radhi, a 35-year-old military contractor who also lives nearby, said after hours of intense shelling, the Houthis seized control of a strategic hill that overlooks both the palace and a key military installation. "The group took control of the area," al-Radhi said.

The Houthis are seen by their critics as a proxy of Shiite Iran and are believed to be allied with former President Ali Abdullah Saleh, who ruled the country for more than three decades before he was ousted in 2012 after Arab Spring protests. While the militants deny any Iran link, their slogan, "Death to Israel, Death to America!" is a variation of a popular Iranian slogan often chanted by Shiite militants in Iraq.

The latest spasm of violence appears to be linked to the Houthis' rejection of a draft constitution that would divide the country into six federal regions. On Saturday, the rebel militiamen kidnapped one of Hadi's top aides, Ahmed bin Mubarak, to disrupt a meeting on the charter. The U.S., Saudi Arabia and other backers of the Yemeni leadership have called for his immediate release.

In a statement Monday, a Houthi spokesman, Mohammed Abdel-Salam, said the charter should only state that Yemen will be a federal state without specifying the number of regions. "Let the wise men of this people agree later on the regions and how to form them and their details," he said.

On Sunday, Hadi issued a statement demanding the army defend the capital, Sanaa, state media reported, though it wasn't clear whether Hadi, who has made similar calls in the past, was ordering the security services to take back control of the city.

Hadi and the Houthis accuse each other of failing to implement a U.N.-brokered peace deal calling for Hadi to form a new national unity government and reform government agencies and for the Houthis to withdraw their fighters from cities. The Houthis have also demanded integration of their militiamen into Yemen's security forces, something Hadi strongly opposes.

"The two sides have hit a dead end," al-Omeisy, the activist, said of the outbreak of violence. "Everyone is strong-headed and everyone has their finger on the trigger. It was only a matter of time."

The prolonged power struggle has undermined Yemen's ability to battle al-Qaida's Yemeni affiliate, al-Qaida in the Arabian Peninsula, and the Houthis' push into predominantly Sunni areas has boosted local support for the terror group.

The al-Qaida affiliate claimed to have orchestrated the attack on the satirical newspaper Charlie Hebdo, saying the assault that killed 12 people was in revenge for cartoons depicting the Prophet Muhammad that were widely seen as offensive.

The group has been linked to a number of failed attacks on the U.S., including a 2009 attempt to down a U.S.-bound jetliner using explosives hidden in the alleged bomber's underwear and a plot the following year to ship bombs concealed in printer cartridges to the U.S. on cargo planes from the Gulf.

The U.S. has provided extensive counterterrorism training and support to Yemeni forces and has targeted al-Qaida with a series of drone strikes in recent years, which have taken out several senior militants but also killed civilians, stoking popular anger.

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Associated Press writers Sarah El Deeb, Maamoun Youssef and Maggie Michael in Cairo contributed to this report.

News from © The Associated Press, 2015