WASHINGTON (AP) -- Al-Qaida's core leadership remains a potent threat, and experts say it has encouraged the terror network's spread into more countries today than it was operating in immediately after the Sept. 11, 2001, terrorist attacks.

President Barack Obama, who ordered the May 2011 raid that killed Osama bin Laden, has described al-Qaida's headquarters as ``a shadow of its former self.'' White House spokesman Jay Carney on Tuesday called it ``severely diminished.''

That bravado didn't match the Obama administration's action this week. It closed 19 U.S. diplomatic outposts stretching across the Middle East, Africa and Asia and evacuated nonessential personnel from the U.S. Embassy in Yemen after intelligence officials said they had intercepted a recent message from al-Qaida's top leader about plans for a major terror attack.

The new communique came from bin Laden's replacement, Ayman al-Zawahri, who as early as December 2001 announced plans to decentralize the network and scatter its affiliates across the globe as a way of ensuring its survival.

Now, major al-Qaida hubs are thriving along the Iraqi-Syrian border, in North Africa and, in the most serious risk to the U.S., in Yemen.

The regional hubs may not take direct orders from al-Zawahri, and terror experts say they rarely coordinate operations or share funding and fighters. But they have promoted al-Qaida's mission far beyond what its reach was a dozen years ago.

``Even while the core al-Qaida group may be in decline, al-Qaida-ism, the movement's ideology, continues to resonate and attract new adherents,'' Bruce Hoffman, director of the Security Studies Program at Georgetown University, wrote in a research paper this year.

Al-Zawahri, an Egyptian whose location is unknown, issues messages to followers every few months that are posted and circulated on jihadi websites. His latest, posted July 30, criticized Obama for the continued U.S. detention of terror suspects at Guantanamo Bay, Cuba, and for launching deadly drone attacks in Pakistan, Afghanistan, Yemen and other Muslim countries.

``You fought us for 13 years. ... Did we soften or toughen up? Did we back out or advance? Did we withdraw or spread out?'' al-Zawahri asked Obama in his message, according to a transcript of his letter that was translated from Arabic by SITE Intelligence Group, which monitors jihadist websites.

He continued, ``I call on every Muslim in every spot on Earth to seek with all that he can to stop the crimes of America and its allies against the Muslims _ in Palestine, Iraq, Afghanistan, Yemen and Mali, and everywhere.''

Three days later, the State Department announced the temporary closing of U.S. embassies and diplomatic outposts _ although not in Iraq, Afghanistan, Israel or Mali. Officials this week said the closures were prompted by an unspecified threat to U.S. and Western interests in a message from al-Zawahri to his top lieutenant in Yemen, where al-Qaida in the Arabian Peninsula is based.

AQAP, as the terror network's regional hub is known, is led by Nasser al-Wahishi, who for years was close to al-Zawahri and bin Laden and is one of al-Qaida's few remaining core leaders, said SITE director Rita Katz.

Intelligence officials say AQAP has for years announced its intent to attack the U.S., and it is widely considered the biggest threat to the West of the al-Qaida affiliates. The group is linked to the attempted Christmas Day 2009 underwear bombing of an airliner bound for Detroit and explosives-laden parcels intercepted aboard cargo flights a year later.

A-Qaida's regional power centers usually have formed in places undergoing political upheaval, where security forces are too distracted to clamp down on extremists.

The civil war in Syria, now in its third year, has given al-Qaida an opportunity to seize land that the Sunni-based network has long yearned to control.

And violence has risen steadily since the U.S. military left Iraq in December 2011. Coordinated jailbreaks at two high-security Iraqi prisons last month set free hundreds of inmates, including al-Qaida extremists. Iraq's branch of al-Qaida, known as the Islamic State of Iraq and the Levant, claimed responsibility for the raids.

Kenneth Pollack, who oversaw Persian Gulf issues while on the White House National Security Council during the Clinton administration, said al-Qaida is poised to gain from instability across the Mideast _ in part by using Iraq as a regional hub.

But the al-Qaida fighters in Iraq and Syria have shown little interest in attacking Americans beyond the region, Pollack said, and neither have most of those in northern Africa, where militants are calling themselves al-Qaida in Islamic Maghreb.

AQIM is rooted in Algeria and affiliated with al-Zawahri, who in April warned French troops fighting extremists in Mali that they would face ``the same fate America met in Iraq and Afghanistan'' as long as they stayed. But there's no evidence the North African groups receive direct orders from al-Zawahri, and most are as motivated by criminal activity as by anti-Western ideology.

An inevitable part of al-Qaida's growth is its new regional leadership _ few of whom fought with bin Laden or have ever worked with al-Zawahri, Katz said.

``In the past, people wanted to go to Afghanistan; it was the dream of every possible jihadi on the front to go to Afghanistan to fight in al-Qaida training camps,'' Katz said. ``You don't see that anymore. No one cares about what's happening in Afghanistan.

``If anyone wants to go anywhere today it is, of course, Syria,'' she said. ``Going to Yemen is always a good thing for them; going to Somalia is less than it used to be, but it's still another possibility. Things change all the time.''