Kofi Annan (File photo)
A U.N. statement says Mr. Annan made telephone calls Tuesday to Congo's president, Joseph Kabila, and his chief rival, Vice President Jean-Pierre Bemba.
Military factions supporting the two candidates began shooting at each other Sunday in the capital, Kinshasa, but the gun battles died down Tuesday after U.N. officials said they had secured a truce. At least five people were killed in three days of fighting.
The U.N. Security Council issued a statement Tuesday backing Mr. Annan's call for an immediate end to the violence, and urged Congolese political leaders to exercise restraint.
U.N. officials in Kinshasa say Mr. Kabila and Mr. Bemba have agreed to withdraw their supporters from the center of Kinshasa, and return them to their original positions.
European nations sent more peacekeepers to patrol the streets of Kinshasa Tuesday. The reinforcements include German and Irish troops.
The fighting began after Congo's electoral commission announced Sunday that Mr. Kabila and Mr. Bemba would face each other in a runoff election in late October.
The commission said neither man won the required majority in Congo's July 30 elections, with Mr. Kabila winning 45 percent and Mr. Bemba taking 20 percent.
About 17,000 U.N. troops are in Congo to keep the peace during the country's first multiparty elections in more than 40 years.
Some information for this report was provided by AP and Reuters.