The capital of Yemen, the Arab world’s poorest and perhaps most chronically unstable nation, has new masters. Shiite rebels man checkpoints and roam the streets in pickups mounted with anti­aircraft 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 the Islamic State militants in Syria and Iraq, Yemen — at the southern tip of the Arabian Peninsula — saw its own sudden, seismic upheaval when Shiite tribesmen known as 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 Lebanon’s Shiite Hezbollah — top power brokers dominating the government and running a virtual state-within-a-state.

Their takeover of the capital also threatens to provoke a violent backlash from hard-line Sunni militants, creating a sectarian battle that would boost al-Qaeda’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, including Syria and Iraq.

Last week, an al-Qaeda 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-Qaeda in the Arabian Peninsula, vowed to fight the rebels and called on other Sunnis for support.

“You will see your bodies scattered and your heads flying,” the al-Qaeda group said in a statement addressing the Houthis.

Yemen’s 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 about a potential pro-Iranian outpost on its border.

In an interview, 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 Houthis 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 Zaydi faith, a branch of Shiite Islam that is almost exclusively found in Yemen and makes up about 30 percent of the country’s population. Zaydi 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 the Zaydi identity.

The rebels, led by 33-year-old Abdul Malik al-Houthi, have 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 Cooperation Council 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,” said Abu Ali al-Hakam, the commander who led the Houthi assault on Sanaa. 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,” Hakam said. “It’s Yemenis from everywhere.”

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 that the two sides — bitter foes in six wars between 2004 and 2010 — shared “temporarily mutual interests.”

— Associated Press