Armed Houthis gather around the wreckage of a vehicle set a blaze by angry protesters after Houthis fired on them in Yemen's central town of Ibb on Feb. 14. (Stringer/Reuters)

The Shiite insurgents who have toppled Yemen’s government are threatening to take over a key oil-producing province to the east of the capital, triggering fears that the country could explode in all-out civil war.

The rebels, known as Houthis, have already seized much of the country’s north with relative ease. But they are likely to encounter stiff resistance if they move into Marib province. Already, the largely Sunni tribes in the region are arming themselves with tanks and rocket-propelled grenades, according to tribal leaders, and the governor has ringed the area with tribal fighters and military units.

“It will be civil war if they come here,” said Mohammed al-Wills, a leader of the Murad tribe in Marib, who has begun coordinating with fellow tribesmen and soldiers to defend the province.

The Houthis say they want to protect residents of Marib from al-Qaeda in the Arabian Peninsula (AQAP), whose fighters have launched periodic attacks in the province. But diplomats and analysts say a conflict could wind up strengthening Yemen’s franchise of al-Qaeda, which has plotted high-profile attacks on the United States. A battle could also draw in tribesmen and Sunni fighters from other provinces.

Sectarian tensions are inflaming the situation. The Houthis follow the Zaydi branch of Shiite Islam, but the majority of Yemen’s 24 million citizens are Sunni. While Yemen has a history of conflict, it has been spared the kind of Sunni-Shiite rivalry that has torn apart Syria and Iraq.

Many Yemenis believe that the Houthi rebels are backed by Iran, a majority-Shiite nation. Neighboring Saudi Arabia — a Sunni powerhouse — has long seen Yemen as within its sphere of influence. Now, Houthi officials and Western diplomats say, Saudi Arabia is providing cash to Marib residents to arm themselves for a confrontation.

“This is becoming a sectarian-driven war because of these outside powers,” said Ali Saif Hassan, a Yemeni political analyst.

The Houthis swept into Sanaa in the fall and effectively forced out the pro-U.S. government of President Abed Rabbo Mansour Hadi last month. The rebels recently seized a military base on the way to Marib, and they have taken over parts of the province to its south, heightening speculation that they might soon move on to the important oil-producing province.

Marib is a strategic prize. Yemen is a small petroleum producer compared with some of its neighbors. But the national government’s budget is overwhelmingly dependent on oil sales. Marib is also home to power plants that provide electricity to Sanaa and other areas of the country, giving whoever controls the province a chokehold over Yemen’s energy supply.

“Everybody’s bracing for a clash there. It’s about the resources,” said a Western diplomat who until recently was based in Yemen and who spoke on the condition of anonymity.

The governor of Marib, Sultan al-Arada, said in a telephone interview that the Houthis had carried out an Iranian-backed “coup” against the Yemeni government. He said his office is coordinating the defense of the province and its oil installations with local tribes as well as military units that are not loyal to the Houthis. He denied that the Saudis were pouring money into the area to parry a rebel advance.

Tribesmen from neighboring regions have pledged to help the province hold off the Houthis, he said.

Escalating violence in Yemen has analysts, diplomats and many Yemenis worried. Here's what led to it, and why you should care. (Gillian Brockell/The Washington Post)

“We have thousands of people from the tribes forming a security belt on the edges of the province, and the military is coordinating with us and preparing to defend us, too,” he said.

The Houthis have called on Arada to step down. Last month, before forcing the resignation of the national government, the insurgents’ leader, Abdulmalik al-Houthi, warned that his fighters could intervene in Marib. He said the potential operation might be necessary to fight al-Qaeda and “support the honorable people of Marib.”

An impoverished state

Located about 75 miles east of the capital, Marib is poor even by Yemeni standards. The government in Sanaa has long been accused by residents of taking the area’s resources but offering few public services in return. In the political void created by the government’s collapse, the role of the area’s already powerful tribes appears to have been strengthened.

Hussein Hazeb, 50, another leader of the Murad tribe, said that tribesmen in the Marib area had armed themselves in part by seizing weapons from a military unit that recently passed through the province.

Some tribal leaders have long received financial support from Riyadh, the Saudi capital, he said, but the recent influxes of cash have been noticeably large.

“All of a sudden you’re seeing people with brand-new pickup trucks and new guns, and you know that they’re getting this from Saudi [Arabia],” Hazeb said.

An official at the Saudi Embassy in Sanaa declined last week to comment on the issue. The embassy closed its operations in Yemen on Friday.

Houthi officials also say that cash is being smuggled from the Saudi border to Marib. The Houthis deny that they are backed by Iran.

Possible gains for al-Qaeda

Analysts, diplomats and many Yemenis fear that the escalating violence could strengthen al-Qaeda’s franchise here by enabling it to portray itself as a champion of the Sunnis. Already, AQAP fighters may be moving from other parts of Yemen into Marib in advance of a fight, diplomats and analysts say.

On Thursday, militants from the radical Sunni group stormed a military base about 60 miles from Marib in a southern province, saying that they wanted to protect it from Houthi attacks.

In Marib, some tribes have fought AQAP, but the extremist group’s sectarian rhetoric appears to be resonating even among those Sunnis who have been its enemies.

The Houthis “are Shiites and they reject Islam,” said Hamed Wahaed, a Marib tribal leader. He has been storing weapons in preparation for a Houthi assault; he boasted by telephone that he owns 10 Toyota pickup trucks mounted with machine guns, two artillery pieces, and rocket-propelled grenades.

He added that Marib has “to fight the Shiite Iranian terrorists.” Still, he said he opposed al-Qaeda and wouldn’t accept its support.

Some tribal officials have threatened to blow up power lines and oil installations in the province to deter a Houthi attack. That would be a serious blow to Yemen’s already weak economy.

“There is no doubt that such an attack on the oil and gas pipelines, as well as on the power plant, will cause a huge crisis for Yemen,” said Hassan Thabet, a professor of economics at Sanaa University.

Wills, the tribal leader, said he opposes damaging the oil and power lines, but he described the threats as a last-resort measure against the Houthis.

“Some of the tribes see this as something like, ‘You may try to take us down, but we’ll take down the whole country if you try,’ ” he said.

Ali al-Mujahed contributed to this report.