SAN’A, Yemen — Attackers armed with automatic weapons, rocket-propelled grenades, and at least one suicide car bomb assaulted the American Embassy in the Yemeni capital today. Sixteen people were killed, including six assailants, officials said.

No Americans were hurt in the deadly attempt to breach the compound walls, which America said bore “all the hallmarks of an Al Qaeda attack.”

Multiple explosions rang out outside the heavily-guarded facility, and gunfire raged for at least 10 minutes at the concrete checkpoints that ring the compound. The dead included six attackers, six Yemeni guards, and four civilians, the state news agency SABA reported. Security officials said people lined up for visas were among those killed or wounded.

It was the deadliest attack on a compound that has been targeted four times in recent years by bombings, mortars and shootings. Yemen, the ancestral homeland of Osama bin Laden, has struggled to put down Al Qaeda-linked Islamic militants, often to the frustration of American counterterrorism officials.

Just last month, the State Department allowed the return of non-essential personnel and family members who had been ordered to leave after a volley of mortars targeted the embassy. The attack instead hit a girls high school next door, killing a Yemeni security guard and wounding more than a dozen girls.

In the 9:15 am attack today, gunmen in a vehicle attacked a checkpoint outside the embassy with RPGs and automatic weapons, Yemeni security officials said. During the assault, suicide bombers in a vehicle made it through the checkpoint and hit a second, inner ring of concrete blocks, and detonated, the officials said, speaking on condition of anonymity because they were not authorized to talk to the press.

SABA, citing an unidentified Interior Ministry official, reported that two suicide car bombs detonated and made no mention of a gunbattle. There was no immediate explanation for the differing accounts. A senior American official in Washington said at least five detonations were heard — but embassy officials spoke of “secondary explosions,” suggesting some could have been RPG blasts.

The Washington official, speaking on condition of anonymity to describe an internal Bush administration briefing, said some of the attackers were dressed as Yemeni troops, and that Yemeni emergency personnel who first rushed to the scene were hit by heavy sniper fire from gunmen who had stationed themselves across the street from the embassy.

Yemeni security officials said a little-known group called Islamic Jihad, unrelated to the Palestinian Arab group of the same name, claimed responsiblity for the attack. But Yemeni authorities have blamed the group in past attacks that have later been claimed by Al Qaeda in postings on the Internet.

In Washington, a State Department spokesman, Sean McCormack, said the embassy’s security upgrades, combined with the response of security officials, stopped the attackers.

Mr. McCormack said the assault had “all the hallmarks of an Al Qaeda attack.”

The explosions hit passers-by and damaged nearby in a nearby residential compound where many Westerners live. Smoke rose from near the yellow concrete blocks that ring the embassy.

An embassy spokesman, Ryan Gliha, told The Associated Press that at least one car bomb detonated. Speaking by telephone from inside the large embassy compound, he could not immediately say if there was any damage to the facility from the blast outside.

At least seven wounded civilians, including children from nearby houses, were taken to the capital’s Republican Hospital, a medical official said, speaking on condition of anonymity because he was not authorized to talk to the press.

One of the Yemeni security officials said the attack had the style of an Al Qaeda operation. The attack highlighted the difficulties Yemen has had in reining in Islamic militants, who operate with considerable freedom in the impoverished country, where much of the mountainous countryside is lawless.

The White House condemned the attacks and offered condolences to the families of the victims.

“This attack is a reminder of the continuing threat we face from violent extremists both at home and abroad,” a White House spokesman, Gordon Johndroe, said.

The American Embassy, in an eastern San’a district, has been targeted repeatedly — through previous attacks have been less organized. Besides the March mortar attack, a gunman opened fire outside the embassy in 2006. He was shot and arrested by Yemeni guards.

In March 2002, a Yemeni man lobbed a sound grenade into the embassy grounds a day after Vice President Cheney made a stop for talks with officials at San’a airport. The attacker was sentenced to 10 years in prison but the sentence was later reduced to seven years.

In 2003, two people were fatally shot and dozens more were injured when police clashed with demonstrators trying to storm the embassy when tens of thousands rallied against the American-led invasion of Iraq.

This year has also seen mortar attacks near the Italian Embassy and a bombing on a compound housing foreigners, neither of which caused casualties.

Washington considers President Ali Abdullah Saleh of Yemen an ally against terrorism, ever since Al Qaeda’s 2000 bombing of the USS Cole destroyer in the port of Aden, which killed 17 American sailors. A similar attack on a French oil tanker two years later killed one person.

But the relationship has frequently been rocky, with American officials grumbling over lax Yemeni detention policies for militants.

A group of 23 Al Qaeda militants escaped from a high-security San’a prison in 2006, amid reports of collusion between security officials and the militants. The American security think-tank Stratfor said in a statement today that Yemen’s security and intelligence services are deepy infiltrated by militants.

Mr. Saleh has also pursued a program letting some militants go free after promising not to carry out attacks.

America was angered when a Yemeni-American, Jaber Elbaneh, convicted in Yemen for planning attacks on oil installations, was freed as he appealed his 10-year prison sentence. Mr. Elbaneh has since been taken back in custody, Yemeni officials say, but San’a has refused American requests that Mr. Elbaneh be handed over to America for trial on charges of provide material support or resources to a foreign terrorist organization.

American officials were also alarmed when Yemeni courts commuted a death sentence for Jamal al-Badawi, convicted of masterminding the Cole attack, giving him instead 15 years in prison.

During a June visit to San’a, President Bush’s homeland security adviser, Kenneth Wainstein, pushed Mr. Saleh for “strong and serious measures to be carried out in Yemeni courts to try the terrorists and to hold them accountable.”