Chadian soldiers have massed along a strategic road in pickup trucks mounted with machine guns as a rebel convoy was spotted heading toward the capital of the volatile African nation.
Usually bustling streets in the capital, N'djamena, quickly emptied at dusk Sunday as rumors flew that the rebels might arrive within hours. Government troops set up roadblocks in Lamidja, about 10 kilometers (6 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.
The competition for power has become more intense since Chad began exporting oil in 2004.
In a radio broadcast Sunday, Chad's communications minister, Moussa Doumgor, repeated accusations that neighboring Sudan is financing the rebels. Sudan has denied the accusations. But Doumgor also added a new dimension to the conflict, accusing Saudi Arabia of supporting the rebels as well.
On Saturday, 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, 885 kilometers (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 UN refugee chief said the violence is threatening aid delivery to the region.
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.