By JEFFREY GETTLEMAN | The New York Times

NAIROBI, Kenya — Abdullahi Yusuf Ahmed, Somalia’s president who has been widely blamed for his country’s deepening crisis, resigned on Monday, casting Somalia into a deeper political abyss, but, at the same time, possibly creating an opportunity.

Mr. Yusuf blamed the international community for not doing enough to shore up Somalia’s transitional government, which has steadily lost control of much of the country to Islamist insurgents. “Most of the country was not in our hands and we had nothing to give our soldiers. The international community has also failed to help us,” Mr. Yusuf told legislators in Baidoa, Somalia’s seat of Parliament.

His exit will most likely kick off an intense, clan-based scramble for his post, which in reality has become increasingly irrelevant as the government has veered toward collapse. Somalia’s transitional government controls only a few city blocks in a country almost as big as Texas and it has been continuously beset by poisonous infighting.

Earlier this month, Mr. Yusuf, who has been president since 2004, tried to fire Somalia’s prime minister but the Parliament refused. Several of Somalia’s neighbors, including Kenya, then threatened to impose sanctions on Mr. Yusuf and his family, accusing Mr. Yusuf of being an obstacle to peace.

Mr. Yusuf, a former warlord who claims to be around 74 years old though he is widely believed to be several years older, has constantly rejected efforts to bring moderate Islamist opposition leaders into the government. Now that he is leaving, many Somalis hope there may be a way to rebuild the government and give the Islamists a meaningful role.

Under Somalia’s transitional charter, the speaker of the Parliament will take over the presidency for one month until the Parliament elects a new president. Several moderate Islamists could be candidates.

Over the weekend, fighting broke out between moderate and radical factions in the first obvious sign of tensions within Somalia’s Islamist community.

On Sunday, a powerful, newly militarized Islamist group declared a “holy war” against the more militant Islamist factions, and it seems to have the muscle to back up its threats. The group, the Ahlu-Sunna Wal-Jama, killed more than 10 fighters from a rival Islamist faction that was known as one of Somalia’s toughest in fighting over the weekend.

The group called on its followers to “prepare themselves for jihad against these heretic groups,” referring to some of the more hard-line factions and “to restore stability and harmony in Somalia and achieve a genuine government of national unity.”

Many analysts had been predicting that exactly this would happen: that as Somalia’s transitional government disintegrated, the Islamist insurgents of varying agendas would begin to slug it out themselves. This weekend’s violence is a strong sign that the infighting is under way.

An episode of grave desecration may have been what started it. In early December, fighters from the Shabab, one of Somalia’s most militant Islamist groups, ransacked the graves of moderate Islamist clerics who had been buried in Kismayo, a town the Shabab controls. On Sunday, moderate Islamist leaders brought this up and condemned the Shabab for such un-Islamic behavior.

“It is a politically motivated act, which can ignite a sectarian war,” warned Sheikh Sharif Sheik Ahmed, one of the moderate Islamists, at a news conference in Mogadishu, Somalia’s capital.

On Saturday and Sunday, gunmen from the Ahlu-Sunna Wal-Jama group took back two towns that the Shabab had controlled, Guri’el and Dhusamareb, and they vowed to roll back recent Shabab gains in other parts of the country. Up until recently, Ahlu-Sunna Wal-Jama was known as a religious brotherhood of moderate Islamists and it did not have a formidable military wing.

Mr. Yusuf did not say what he will do now but many Somalis expect that he will return to his clan stronghold in northern Somalia. His militia has already fled the capital, with more than 100 soldiers loyal to Mr. Yusuf flying out on Sunday for northern Somalia. Several Somali politicians aligned with Mr. Yusuf also left for northern Somalia on Sunday, implying that Mr. Yusuf’s powerful sub-clan, the Majerten, may be pulling out of the government.