WASHINGTON — Yemen, the site of a car-bomb attack yesterday on the American Embassy, is quietly emerging as a base for Al Qaeda veterans of the Iraq war, who are seeking refuge there and are close to establishing the kind of safe haven the group enjoys on Pakistan’s border with Afghanistan.

American intelligence officials believe that Osama bin Laden’s organization is regrouping in the governorates of Ma’rib, al-Jawf, and Hadhramaut along Yemen’s border with Saudi Arabia, and that Al Qaeda in Yemen is now being led by a former military aide to Mr. bin Laden, Nasir al-Wahishi.

“The foreign-fighter flow in Iraq has slowed down to a trickle,” a retired four-star general and adviser to Multi-National Force-Iraq, General Jack Keane, told The New York Sun. “They can’t get to their operational cells to be a bomber or a fighter, so some of them are going to other safe havens. A lot of this has to do with where they came from. But two of the places certainly are Pakistan and Yemen.”

That assessment was supported by two American intelligence officials whom the Sun contacted for comment on the bombing of the American Embassy yesterday in Sana’a. The attack killed 16 Yemeni nationals but no Americans, the Associated Press reported, and the attackers included at least one suicide bomber, as well as gunmen wearing Yemeni military uniforms and armed with rocket-propelled grenades. One of the tasks of the FBI, which will investigate the attack, will be to determine whether members of Yemen’s armed forces participated in the attack.

“This attack is a reminder that we are at war with extremists who will murder innocent people to achieve their ideological objectives,” President Bush said yesterday after a meeting with General David Petraeus.

Elements of Yemen’s security services, which America has trained and subsidized since the terrorist attacks of September 11, 2001, may indeed have had a hand in yesterday’s bombing. In April, one of the FBI’s most wanted terrorism suspects, Jaber Elbaneh, arrived at a Sana’a courtroom that was hearing the case against another Al Qaeda associate and denounced the court, only to walk free moments later, the Washington Post reported. Court officials refused to arrest and extradite him. Meanwhile, special religious vice committees have emerged in Yemen’s lawless northern provinces bordering Saudi Arabia, according to the Guardian and Arabic newspapers.

President Saleh, for his part, pardoned the mastermind of the 2000 USS Cole bombings in Aden, Jamal al-Badawi, last October after he escaped with Mr. Wahishi from a high-security prison.

The recent developments in Yemen echo those in Pakistan, where Al Qaeda’s central leadership has re-established a base of operations in the tribal provinces that border Afghanistan. In Pakistan, as in Yemen, the will of the country’s leadership to prosecute the war on terrorism has faltered. In 2006, the Pakistani military effectively stopped fighting Al Qaeda and the Taliban in the tribal provinces.

A former American ambassador-at-large for counterterrorism, Michael Sheehan, said that Yemen, Mr. bin Laden’s ancestral homeland, is no longer concentrating on the fight against Al Qaeda. “Their focus has been slipping over the past several years,” he said. “You have the embarrassing escapes and releases of people. That is worrisome. You have a potential sanctuary developing there again. This is a wake-up call: It could get worse. But the good news is their operational capability is very poor.”

Mr. Sheehan noted that yesterday’s attack failed to kill any Americans but claimed the lives of innocent Muslims, an outcome that will likely hurt Al Qaeda’s effort to gain supporters in the Islamic world. “Al Qaeda failed again,” he said. “This is a miserable attack for them. It killed no Americans, it only killed innocent Muslims. Compare that to 1998, when they blew up two American embassies, or in 2000, when they sank a warship.”

Mr. Sheehan, who served between 2003 and 2006 as the deputy commissioner for counterterrorism at the New York City Police Department, said Mr. Saleh’s prosecution of a war against Al Qaeda presents a political challenge for the Yemeni leader. “In these cycles of ups and downs in counterterrorism cooperation, there is a political problem in beating up the Islamic groups that are associated with the violent elements,” he said. “They lose interest because they don’t want to pay a political price with this constituency.”