Loudspeakers mounted on pickup trucks regularly blare a message of defiance above the steady din of honking horns and grinding motors.

"Beware of the West!" warns the amplified voice, echoing amid traffic-clogged streets and bustling shops. "The West doesn't have Yemen's interests at heart."

The Yemeni capital, roiled in recent years by mass protests, car bombings and gun battles, is at the center of profound disquiet about what the future holds for this strategically situated nation of 24 million, long a key partner in U.S. counter-terrorism efforts against Al Qaeda.

An uneasy and tenuous calm hangs over this ancient town nestled amid scorched desert peaks. The loudspeakers, like the ubiquitous anti-U.S. slogans stenciled on walls and the teenage gunmen running checkpoints, are manifestations of Sana's newest rulers: the Houthis, a provincial faction turned national kingmakers in a dramatic turn of events that has alarmed Washington and its Persian Gulf allies.

Although many at home and abroad have denounced the Houthis, who dissolved Yemen's parliament this month, the group has won considerable popular support through pledges to destroy archenemy Al Qaeda and curb rampant corruption.

The Houthis' ascendance has also signaled the abrupt breakdown of years of U.S.-backed efforts to craft a transition to a democratic, pro-Western government after decades of autocratic rule that crumbled amid "Arab Spring" protests. United Nations Secretary-General Ban Ki-moon declared ominously last week that Yemen is "collapsing before our eyes."

Improbably calling the shots in Sana these days is a Shiite Muslim-led minority movement aligned with Shiite Iran, where the media gloat about Tehran's expanding influence in Arab capitals, from Sana to Beirut, Damascus to Baghdad. While emphasizing that they are not pawns of Tehran, the Houthis do not conceal their esteem for Iran and Hezbollah, the Iranian-backed Shiite movement that is a dominant military and political force in Lebanon.

"We didn't need the help of Iran or Hezbollah to take over Sana," Mohammed Bukhaiti, a top Houthi political officer, said during an interview Thursday at the group's compound in a north Sana neighborhood. "We have our own weapons, and we are better fighters than either of them.... But what we have in common with Iran and Hezbollah is a desire to confront the American plans for the region."

Bukhaiti and other Houthi leaders said they favored continued diplomatic relations with Washington, despite strong objections to U.S. policies in the Mideast, especially Washington's support for Israel.

The Houthis, who say their aims are democratic, have placed U.S.-backed President Abdu Rabu Mansour Hadi and his Cabinet under house arrest while they establish a presidential council to run Yemeni affairs on an interim basis.

Citing security concerns and instability, the United States and other Western nations last week withdrew diplomatic missions from Sana. The Houthis denounced the move, at a moment when the capital is relatively secure, as a transparent effort to scare off international investors and donors from the Arab world's poorest nation and force the group to relinquish power.

Washington and the Houthis share a common foe: Al Qaeda. But, from the Houthis' standpoint, the U.S. drone strikes targeting Al Qaeda and the resulting civilian casualties are counterproductive measures that serve as recruiting tools for the terrorist network and are a violation of Yemeni sovereignty.

"For us, fighting Al Qaeda is an existential issue," said Bukhaiti, a former political refugee in Canada and the Netherlands who wore traditional Yemeni dress, including a curved dagger in his belt. "We are serious about fighting Al Qaeda. America is not."

Yemen is home to Al Qaeda in the Arabian Peninsula, considered among the terrorist network's most potent affiliates. Despite Houthi advances, many see Al Qaeda militants gaining in largely Sunni Muslim areas of Yemen by portraying themselves as guardians of the nation's Sunni majority against a Houthi Shiite onslaught.

Militants last week overran an army base in the southern province of Shabwa, an Al Qaeda stronghold.

"The Houthi takeover has resulted in Al Qaeda's best recruitment drive in years," said Ahmed Zurqah, an analyst opposed to the Houthis. "Tribal youths are also signing up to fight against the Houthis."

Yemen has largely been spared the Sunni-Shiite bloodletting that continues in Iraq and Syria.

Some have likened the Houthis to Hezbollah. But, unlike the Houthis, Hezbollah has never moved to seize outright control of the Lebanese government, which operates on a sectarian power-sharing arrangement. Even some former Houthi supporters call the group's power grab a reckless foray for a minority movement based in the north with core support among about a third of the population.

"The Houthis have overstretched themselves," said Ali Bukhaiti, the leftist brother of Mohammed Bukhaiti who broke with the Houthis after the takeover. "They are warriors but don't have political acumen. And like all religious groups they believe that God will intervene. But God does not provide salaries at the end of the month."

The Houthi ascendance is the equivalent of a geopolitical body blow for oil-rich Saudi Arabia, which has clashed with the Shiite group along the nations' border.

Since the Houthi takeover, the Saudi government has pulled financial aid from Yemen and is reportedly arming anti-Houthi tribes. Saudi officials, locked in a struggle for regional dominance with Iran, view a pro-Iran beachhead on their border with great distress, diplomats say.

Although Sana is firmly under Houthi control, there is rising tension in outlying areas where the population is mostly Sunni Muslim.

Saudi Arabia-backed tribal factions and Al Qaeda elements are reported to be preparing to repel any Houthi advance into Marib province, an oil and energy hub east of Sana.

In the south, where Houthi support is thin, antigovernment activists have formed armed "popular committees" amid renewed talk of secession.

Some fear that Yemen could spiral into all-out civil war and proxy conflict, a Syria-like conflagration with outside powers arming preferred factions.

Others see the makings of a national breakup in a complex, tribal-driven nation where north-south tension has never completely abated. (North and South Yemen were separate nations before merging in 1990.)

Last week, U.N. special envoy Jamal Benomar told the Security Council that the nation was at a critical crossroad.

"Either the country will descend into civil war and disintegration, or the country will find a way to put the transition back on track," the envoy said.

In Sana, however, life mostly proceeds at a normal pace. Truckloads of young Houthi militiamen armed with rifles and rocket-propelled grenade launchers occasionally rumble through the streets, but few take much notice. Many people are well aware that the respite could be short-lived.

"It's true that the Houthis have brought stability here," said Maqdad Sabanah, 22, a shopkeeper in the capital's sublime Old City, a U.N. World Heritage site renowned for its singular multi-story buildings and narrow passageways. "But there's also a lot of uncertainty now. No one knows what's going to happen."

LA Times