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Hani Mohammed, Associated Press
Yemeni protesters burn representations of American, French and Israeli flags during a demonstration to show their support for Houthi Shiite rebels in Sanaa, Yemen, Friday, Jan. 23, 2015. Thousands of protesters demonstrated Friday across Yemen, some supporting the Shiite rebels who seized the capital and others demanding the country's south secede after the nation's president and Cabinet resigned.

SANAA, Yemen — Yemen's Shiite rebels faced mounting pressures and signs of internal divisions Friday after the U.S.-backed president and his cabinet resigned rather than submit at gunpoint to their increasing demands for greater power.

With thousands of demonstrators on both sides taking to the streets across the impoverished Arab country, the rebels appeared wary of the dangers of overstepping in Yemen's minefield of tribal politics, sectarian divisions, al-Qaida militancy and a strong secessionist movement.

Although rebel gunmen manned checkpoints throughout the capital and continued besieging the houses of government ministers, they made no public attempt to fill the vacuum created by the resignations of President Abed Rabbo Hadi, his prime minister and cabinet. And there were signs that the national parliament would reject the resignations when it meets Sunday.

Indeed, it seemed as though the rebels, known as the Houthis, do not want to rule the country outright and would prefer that Hadi remain as a figurehead president.

In his latest speech, rebel leader Abdel-Malek al-Houthi vowed to keep up the pressure until the government meets all his demands, including greater representation in government ministries and in a committee to rewrite the country's constitution. He stressed his group's opposition to dividing the country into six regions — a measure in the draft constitution that would diminish the resources under the Houthis' control.

Yemeni law dictates that the parliament speaker — Yahia al-Rai, a close ally of former autocratic ruler Ali Abdullah Saleh — will now assume the presidency. Saleh, who stepped down in 2012 a year after widespread street protests, still wields considerable power and is believed to be allied with the Houthis.

"The strong majority of people are against Houthis' expansionist move," said political analyst Omar Abdel-Aziz. "Pressure from different regions on them right now are mounting."

The Houthis were also confronted with dissent from within their own ranks. Ali al-Bukhaiti, a prominent member of the group's political arm, resigned Friday.

In a statement posted on his Facebook page, al-Bukhaiti the Houthis had become "the official authority" in the country. He said he wanted to work as a mediator to "lessen the political polarization which is transforming into a regional and sectarian polarization that threatens the whole nation with fragmentation."

Even before the Houthis' recent ascendance, a powerful movement in southern Yemen was demanding autonomy or a return to the full independence the region enjoyed from 1967 to 1990. Southerners outrightly reject rule by the Houthis, whose power base is in the north.

On Friday, thousands of demonstrators in the southern city of Aden raised the former flag of Southern Yemen over the local airport and security headquarters building, witnesses said. Top officials in Aden and the southern province of Shabwa both announced that they would no longer follow orders from the capital. Thousands more protested against the Houthis' "coup" in several other cities, including Taiz, Ibb and Houdida.

But tens of thousands also turned out in the capital, Sanaa, in support of the Houthis, converging on the airport road. They raised green flags and banners proclaiming their slogan — "Death to America, death to Israel, a curse on the Jews and victory to Islam" — a variation of a popular Iranian slogan often chanted by Shiite militants in Iraq and supporters of Lebanon's Hezbollah.

The Houthis have always been careful not to frame their goals in sectarian terms. A leading Houthi politician, Hamid al-Bukhaiti, described the rallies as a public outcry against "corruption and political crime."

Nevertheless, the fast-moving events have fanned fears of a sectarian conflict that could fuel support for al-Qaida, a Sunni movement that has links to some of the country's tribes and is at war with both the Shiites and Hadi's forces. U.S. officials say the developments are already undermining military and intelligence operations against al-Qaida's Yemen-based affiliate, which made its reach felt in this month's deadly Paris attacks.

Some observers are also raising the specter of a proxy battle in Yemen between regional powers Saudi Arabia and Iran, a Shiite country believed to fund the Houthis. Saudi Arabia, which has long been Yemen's economic lifeline, cut most of its financial aid to this country after the Houthis seized the capital in September. The Houthis are Zaydis, a Shiite Muslim minority sect that makes up about a third of Yemen's population; the rest of Yemen is overwhelmingly Sunni Muslim, as are the Saudis.

The political turmoil and loss of Saudi funding threatened a humanitarian crisis. The international aid group Oxfam, which has been working in Yemen for more than 30 years, warned Friday that the country is on "the brink of humanitarian disaster with millions of lives at risk." Half of the country's population is in need of humanitarian aid, and nearly a million Yemeni children suffer malnourishment, the report said. The group urged the international community to help end the conflict.

U.N. envoy Jamal Benomar was "in deep discussion mode" and in touch with various players, a spokesman for the U.N. secretary-general, Stephane Dujarric, told reporters Friday. "It's a very unstable time in the capital, and he's really making the rounds" and trying to meet with as many people as possible.

President Hadi, a U.S. ally in its campaign against Yemen's local al-Qaida branch, stepped down as president along with his Cabinet on Thursday days after gunbattles began rocking the capital. The Houthis had taken over the presidential palace and positioned their fighters at the doorsteps of Hadi's house.

While in the Houthis' captivity, Hadi signed a deal by which he pledged political concessions to the rebels in return for their withdrawal from his house and presidential palace and the release of his top aide, whom they'd abducted. The deal was not put into effect, and the Houthis demanded more concessions including top posts in the government, according to Hadi's aides.

In Washington, State Department spokeswoman Jen Psaki said U.S. officials have been in touch with a "full spectrum of political leaders" in Yemen.

"The Houthis are a legitimate political constituency in Yemen and have a right to participate in affairs of the state," Psaki said. "We urge them to be a part of a peaceful transition process. That said, we condemn their use of violence and are concerned by their non-compliance with agreements they have been signatories to."

Much of the focus now is on Sunday's parliament session. According to outgoing constitution, al-Rai, the parliament speaker, would serve as president in the absence of a vice president until holding early presidential elections. The southern bloc in parliament called for a boycott of the session.

Representatives of various political parties held a meeting with Houthi representatives in an attempt to achieve a consensus. Most demanded the "rejection" of Hadi's resignation, according to a politician who spoke on condition of anonymity because he was not authorized to discuss the discussions.

He said the Houthi representative declined to give a clear stance, while the party of Saleh, Yemen's powerful former autocratic ruler, insisted on accepting the resignation and holding an early vote.

Michael reported from Cairo. Associated Press reporters Matthew Lee in Washington at Cara Anna at the United Nations also contributed.