The capital of Yemen, the Arab world's poorest and perhaps most chronically unstable nation, has new masters. Anti-American Shiite rebels man checkpoints and roam the streets in pickups mounted with anti-aircraft guns. The fighters control almost all state buildings, from the airport and the central bank to the Defense Ministry.

Only a few police officers and soldiers are left on the streets. Rebel fighters have plastered the city with fliers 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.

While the world has been focused on the fight against Islamic State militants in Syria and Iraq, Yemen at the southern tip of the Arabian Peninsula has seen its own sudden, seismic upheaval when Shiite rebels known as the Houthis overran Sanaa two weeks ago.

Now the Houthis, who many believe are backed by Shiite-led Iran, are poised to become Yemen's version of the Shiite Hezbollah in Lebanon — top powerbrokers dominating the government and running a virtual state-within-a-state.

Their takeover of the capital also threatens to bring a violent backlash from hard-line Sunnis, creating a sectarian battle that would boost al-Qaida's branch in Yemen, which the United States has been battling for years in a drone campaign and in coordination with the Yemeni military. The rallying cry of fighting against Shiite power could turn Yemen into a magnet for Sunni jihadis from around the region, like Syria and Iraq.

Last week, an al-Qaida suicide bomber rammed an explosives-laden car into a hospital used by the Houthis in Maarib province, killing one person. The group, known as al-Qaida in the Arabian Peninsula, vowed to fight the rebels and called on other Sunnis to support it.

"You will see your bodies scattered and your heads flying," al-Qaida said in a statement, addressing the Houthis.

The U.S.-backed president, Abed Rabbo Mansour Hadi, is largely helpless, struggling to form a new government to meet the Houthis' demands. Neighboring Saudi Arabia is worried over a potential pro-Iranian outpost on its border.

In an interview with The Associated Press, Jamal Benomar, the U.N. special envoy who has been mediating among the government, the Houthis and other factions, warned that "this takeover of Sanaa by the Hawthis will widely reverberate in Yemen and the region."

"Yemen will now be seen as linked to other situations in the region, with regional and international involvement," he said.

The Houthis, who call themselves Ansar Allah, Arabic for "Supporters of God," are followers of the Zaidi faith, a branch of Shia Islam that is almost exclusively found in Yemen and makes up about 30 percent of the country's population. Zaidi religious leaders ruled much of northern Yemen for centuries — and the Houthis, backers of the Houthi family, a clan that claims descent from the Prophet Muhammad, have sought to revive Zaidi identity.

The rebels, currently led by 33-year-old Abdul-Malik al-Houthi, fought a series of civil wars since the mid-2000s from their stronghold of Saada north of Sanaa. In 2011, they took complete control of Saada province.

But their advances this year have been startling. They swept south, defeating Sunni tribesmen loyal to the conservative Sunni Islah party, and in July captured Amran province, which borders the capital. They then overran the capital itself on Sept. 21 as the military largely collapsed.

The Houthis present themselves as seeking to achieve the goals of the 2011 Arab Spring uprising that led to the overthrow of longtime autocrat Ali Abdullah Saleh. They reject a Gulf-brokered deal that led to Saleh stepping down and Hadi taking his place because it largely splits power between Saleh's supporters and the Islah party, which is the Muslim Brotherhood's branch in Yemen.

Instead, they say, they want a broader government that includes their movement and southern Yemenis, who have long sought independence. And they want implementation of a plan reached by political parties in January to give greater autonomy to Yemen's regions.

"We are not a group isolated from the rest of the country. We are part of the social fabric," Abu Ali al-Hakam, the commander who led the Houthi assault on Sanaa, told AP. He spoke as he visited the captured headquarters of the army's 1st Armored Division, an elite outfit with close links to the Islah party. It had spearheaded army campaigns against the Houthis.

"It is not just the Houthis who are controlling Sanaa now, its Yemenis from everywhere," said the diminutive al-Hakam after receiving a hero's welcome by his fighters.

The Houthis were quick to tap on the widespread grievances to show themselves as a feasible alternative.

"I and my family feel safer now," said Faraj al-Raeeny, a schoolteacher from mainly Zaidi Amran province. "The Houthis resolved many disputes and put right many injustices. They strictly enforce order."

Still, not all Zaidis back the rebels, and the takeover is likely to only polarize a nation where the central government is chronically weak. Much of the country is out of government control, plagued by tribal divisions, al-Qaida militant violence, widespread corruption and deep poverty that breeds resentment or rebellion.

The scene is further complicated by political rivalries. Hadi's supporters have long accused Saleh loyalists, who still hold key posts in the military, security forces and government, of undermining Hadi in a bid to return to power.

Saleh and his loyalists in the army are widely believed to have helped the Houthis by standing aside as the fighters swept into Sanaa.

Ali al-Imad, a senior Houthi official, denied there were any "understandings" struck with Saleh's camp, but he acknowledged in an interview with the AP that the two sides — bitter foes in six wars between 2004 and 2010 — shared "temporarily mutual interests."

Hadi appeared caught off guard. After Amran was captured in late July, Hadi met with politicians who warned him that the Houthis would move on Sanaa next. "He said he was convinced that the Hawthis will not come near Sanaa," rights lawyer Baraa Shiban, who attended the meeting, told AP.

A new, U.N.-brokered accord that was hurriedly signed on the day Sanaa fell to the Houthis calls for a new government, for all armed factions to put down their arms and for the rebels to leave the capital. But there is little sign that will happen.

"This peace agreement must be implemented, otherwise the prospect of the disintegration of Yemen as we know it will become real," warned Benomar, who negotiated the accord.

Many doubt the Houthis have the need or resources to grab more territory. But they have virtual veto power over who becomes the next prime minister and over the makeup of the next government.

And they are locking in their forces' position in the capital — emulating the model of Iranian-backed Hezbollah, which in Lebanon is the de facto government in predominantly Shiite areas of southern Beirut and in the south and east of the country.

In Sanaa, the Houthis have tightened their grip on the city's northern districts where Zaidis are dominant, as well as the nearby international airport. Tanks and armored vehicles looted from army bases have now been deployed in those areas.

After the fall of Sanaa, Houthis staged a massive victory rally in the city, flying Hezbollah flags and portraits of Iran's late supreme leader Ayatollah Ruhollah Khomeini.

"It is very clear that Hezbollah is their model. They will never give up control of the airport or the northern districts," Mohammed Qahtan, a senior Islah leader, told the AP in a hotel apartment where he has lived since his Sanaa home was stormed by the rebels.