LAMIDJA, Chad -- Chadian soldiers in heavily armed pickup trucks were massing along a strategic road Sunday as a rebel convoy was spotted heading toward the capital of this volatile central African nation.

As dusk fell in the capital, N'Djamena, usually bustling streets quickly emptied as rumors flew that the rebels might arrive within hours. Government troops set up roadblocks in Lamidja, about six miles from the capital, and were searching cars and fighting-age men.

The Forces for Democracy and Development, known by the French acronym UFDD, is a union of several rebel groups opposed to President Idriss Deby, who first took power at the head of his own rebel army in 1990. The group has had sporadic clashes with the government since 2005 and launched a failed attack on the capital in April.

In a radio broadcast Sunday, Chad's communications minister, Moussa Doumgor, repeated accusations that neighboring Sudan is financing the rebels. He also added a new dimension to the conflict, accusing Saudi Arabia of supporting the rebels, as well. Sudan denied the accusation.

On Saturday, the rebels launched an attack and claimed to have seized Abeche, the largest city in the country's volatile east, but pulled out Sunday before government troops arrived. A U.N. agency report confirmed that a rebel convoy had been spotted crossing a village west of Abeche, driving toward the capital on the sole highway linking the two regions.

Abeche, 550 miles east of the capital, is the base for dozens of aid organizations looking after 200,000 refugees from Sudan's Darfur and 50,000 displaced Chadians. The U.N. refugee chief said the violence is threatening aid delivery.

It was not clear if there were casualties in Saturday's attack; communications were cut to Abeche soon after the fighting began and calls to government officials in the capital were not returned.

The government has said the violence pitting ethnic Arabs against ethnic Africans appears to be between Chadians, but accused Sudan of instigating the clashes. Chad often accuses Sudan of supporting Chadian rebels, and Sudan makes a similar accusation against Chad.

In Darfur, ethnic African tribes accusing the central government of neglect launched a rebellion three years ago, following years of low-level tribal clashes over land and water. The government is accused of responding by unleashing ethnic Arab tribal militias who have been linked to atrocities.

More than 200,000 people have died and 2.5 million have been displaced since fighting began in Darfur in early 2003.

Arabs, among them slave traders, first reached sub-Saharan Africa more than a century ago. Intermarriage and the embrace of Islam by many Africans have blurred identities, but an Arab-African divide persists. It is exacerbated by a lack of resources in the region, pitting communities against each other in a competition for water and land.