Experts say the audiotape, posted on an Islamist website Friday, and other recent recordings indicate that al-Qaeda is intensifying its focus on the Horn of Africa where the terror network has a long history of operations.
The recording came as Somali government forces backed by Ethiopian troops prepared to launch a major assault on the last stronghold of Somalia's Islamic militias, while the U.S. Navy deployed off the coast to keep al-Qaeda and allied militants from escaping the war-wrecked country.
The militia, which has been driven from the capital, Mogadishu, and much of the south, have vowed to launch a guerrilla war as part of a bloody reprisal.
"I call upon the Muslim nation in Somalia to remain in the new battlefield that is one of the crusader battlefields that are being launched by America and its allies and the United Nations against Islam and Muslims," Osama bin Laden's deputy Ayman al-Zawahri said in the audiotape.
"Launch ambushes, land mines, raids and suicidal combats until you consume them as the lions and eat their prey," the Egyptian-born al-Zawahri said. He also urged Muslims in other Mideast and African countries to support the Islamists battling the troops from Ethiopia, a country with a large Christian population.
The recording, which was more than five minutes long, could not immediately be verified but was aired on a website frequently used by militants. It carried the logo of al-Qaeda's media production wing, as-Sahab. It was the first recording by al-Zawahri this year and his third in less than a month.
In an audiotape released last week, al-Qaeda's No. 2 encouraged Islamic militants in Somalia to "be firm in defense of the honor of Islam." Last year, bin Laden also identified Somalia as a battleground in his war with the West.
al-Qaeda has increasingly discussed Africa in messages released over the past year. In an April videotape, Osama bin Laden called on Islamic militants to battle any Western troops deploying in the war-torn Darfur region of Western Sudan. Bin Laden was based in Sudan during the 1990s until the government ousted him briefly before a U.S. airstrike on a Sudanese factory in retaliation for the 1998 al-Qaeda bombings of the U.S. Embassies in Kenya and Tanzania.
Ben Venzke, head of the U.S.-based IntelCenter, which monitors terrorism communications, said these recordings indicate an increased al-Qaeda emphasis on Muslim Africa.
"This is a clear indication of their priorities and focus," Venzke said. "They are preparing way in advance. ... And it just shows that their sense of timing and planning is very different than American sensibilities," he said. "They are not going to tell you date and time of an attack, but they do consistently tell you what their focus is on."
The United States and others have expressed concern about al-Qaeda's growing influence in Somalia. Three al-Qaeda suspects wanted in the East African U.S. embassies bombings are believed to be leaders of the Islamic movement in Somalia. The Islamists deny having any links to terror networks.
A senior U.S. State Department official has said that al-Qaeda militants were operating with "great comfort" in Somalia. Jendayi Frazer, who heads the department's Africa bureau, said a top U.S. goal is to capture the three militants wanted for the 1998 embassy bombings and a 2002 attack against a hotel in Kenya.
Ismael Mohamoud Hurreh, a member of Somalia's transitional government, also warned that many senior al-Qaeda figures who spent time in Sudan or Somalia in the 1980s and 1990s aimed to return and establish Somalia as a base.
In Friday's recording, al-Zawahri told the Somali militias not to be intimidated by the United States, saying America's struggle with insurgents in Afghanistan and Iraq have paved the way for the militants' victory. He also reminded the guerrillas that the U.S. and United Nations previously were defeated in Somalia.
A U.N. peacekeeping force, including U.S. troops, deployed in Somalia in 1992 but the experiment in nation-building ended the next year when fighters loyal to a Somalian clan leader shot down two U.S. Army Black Hawk helicopters and battled American troops, killing 18 servicemen.
"My brother Muslims in Somalia, don't be traumatized by America's force because you have defeated it previously with the support of Allah, and it is weaker today than before," al-Zawahri said in the audiotape.
Rita Katz, director and co-founder of the SITE Institute, an independent group that provides counterterrorism information to the U.S. government, said the recording showed that the battle in Somalia and situation in other African countries increasingly mattered to the mostly Arab terror group.
"All these places mean a lot to al-Qaeda," she said. "It's very important for them to rise up and revive al-Qaeda's footsteps in these countries."