Chadian rebels renewed their assault on the capital of this oil-rich central African country Monday, and tens of thousands of people fled as gunfire crackled and artillery shells exploded across the city. The third day of fighting in N'Djamena threatened to further destabilize an already violent swath of Africa that is home to hundreds of thousands of refugees, the Associated Press reported. Hours after the rebels went back on the attack following an overnight retreat, the U.N. Security Council authorized France and other nations to help Chad's government. France has 1,800 soldiers backed by fighter jets based in its former colony, but French officials said there were no immediate plans to take on the insurgents. Referring to the U.N. authorization, Foreign Minister Bernard Kouchner said, "I hope that we won't have to use it." Officials from the Republic of Congo and Libya were expected to arrive Tuesday as part of an African Union mediation plan.