The suicide bombing in Mogadishu, Somalia's war-scarred capital, that killed more than 100 people indicates that Arab and transnational fighters in the Islamist al-Shabaab organization are pushing to extend global jihad to the Horn of Africa.

This faction of the Islamist group has frequently been at odds with the mainstream nationalist contingent that seeks to topple the Western-backed Transitional Federal Government.

It was set up in December 2006 after a U.S.-supported invasion by neighboring Ethiopia brought down a short-lived Islamist regime.

The internal squabbling intensified when al-Shabaab unexpectedly withdrew its forces from Mogadishu in August in the face of a major offensive spearheaded by a 9,000-strong African Union "peacekeeping force" known as Amisom.

The transationalist fighters, including hardened veterans of the battles in Afghanistan, Pakistan and Iraq, were pulled back to the southern coastal city of Kismayo, a longtime sanctuary for the foreign jihadists, to regroup.

Tuesday's suicide attack using a truck bomb bears all the hallmarks of die-hard jihadists, who are commanded by Ibrahim Haji Mead, aka Ibrahim al-Afghani, and Ahmad Abdi Godane, aka Abu Zubair.

These fighters introduced suicide bombings in Somalia in 2007 and have used them with withering effect.

Tuesday's bombing was the deadliest single bombing since al-Shabaab launched its insurgency five years ago.

The attack, carried out by a dropout identified as Bashar Abdullahi Nur, took place near the Education Ministry where students and their families had gathered to register for scholarships offered by the Turkish government.

The truck was packed with mortar shells, fuel drums and chemical-filled plastic containers, the privately owned Somali Shabeelle Media Network Web site reported.

Many of the victims were seen running around the blast scene covered in flames and screaming for help.

In 2009, 24 people, including three TFG ministers, were killed in a suicide bombing at a Mogadishu graduation ceremony.

Al Shabaab carried out its first suicide attacks outside Somalia in July 2010 in Kampala, capital of neighboring Uganda.

Seventy-six people died in twin bombings as they watched the World Cup soccer final on television. Uganda and Kenya contribute most of the troops in Amisom.

"Despite the pullback, leaders of the transnational faction … continue to espouse jihadist ideology, indicating that residual forces in Mogadishu will continue to conduct militant operations there," the global security think tank Stratfor observed.

"The group still poses a serious threat," particularly in Mogadishu, a sprawling city on the Indian Ocean with a population of 2 million that is riddled with al-Shabaab sympathizers and, no doubt, stay-behind sleeper cells as well.

"With 9,000 AU peacekeepers and a few thousand TFG soldiers, Amisom and the TFG lack the forces, equipment and training to fully patrol the city, let alone secure it against such operations.

"Even U.S. troops have not been able to able to completely lock down cities such as Baghdad and Kabul, so there is not much chance that Amisom and the TFG will be able to prevent attacks in chaotic Mogadishu," Stratfor observed.

Attacks like Tuesday's guarantee that the capital remains gripped by fear and uncertainty while al-Shabaab reorganizes in its havens in the south and center of the Horn of Africa state.

Somalia has been without a functioning central government since 1991 when the dictator Siad Barre was overthrown by clan warlords who have torn the country apart.

In recent weeks, the CIA and the U.S. military's Joint Special Operation Command have stepped up attacks on al-Shabaab chieftains with missile-armed unmanned aerial vehicles.

This has coincided with a sharp escalation in airstrikes against jihadists of al-Qaida in the Arabian Peninsula in Yemen, across the Gulf of Aden from Somalia.

U.S. intelligence says AQAP wants to join forces with al-Shabaab, or at least the transnational faction, to intensify their operations in the Horn of Africa, East Africa and the Arabian Peninsula, particularly Saudi Arabia.

Amid growing clashes in Yemen between forces loyal to President Ali Abdullah Saleh and rivals seeking to oust him, AQAP has been seizing territory in the south that could be used to launch operations, including attacks on the United States.

The Americans have recently established a ring of UAV bases around the Horn of Africa and the Arabian Peninsula from which to widen their drone war.