NAIROBI, Kenya — Sudan cut diplomatic ties with Chad yesterday after accusing its neighbor of backing an audacious rebel attack on the Sudanese capital.

Sudanese officials claimed to have crushed the assault on Khartoum by a Darfur rebel group known as the Justice and Equality Movement, or JEM, which crossed hundreds of miles of desert in armored pickups and struck the Omdurman suburb of the capital Saturday.

Yesterday morning, President al-Bashir of Sudan, appearing on state-run television in military fatigues, said the rebels had been “totally destroyed.”

“These forces come from Chad, who trained them,” Mr. Bashir said, according to the Reuters news agency.

“We hold the Chadian regime fully responsible for what happened. We have no choice but to sever relations,” he added.

Analysts say there were several layers of interests at work in the attack.

It is likely to alter the already tangled process of reaching a settlement to end the crisis in Sudan’s western Darfur region, where the government and a militia known as the Janjaweed have waged a five-year campaign of violence against civilians and numerous rebel groups.