Soldiers in Guinea-Bissau have launched a coup attempt, taking over roads, TV and radio stations, and government offices in the country's capital.

The unrest began late Thursday, the night before campaigning was due to begin for a presidential run-off election.

Soldiers attacked the homes of interim President Raimundo Pereira and former Prime Minister Carlos Gomes Jr. Gomes is the front-running presidential candidate but is known to be unpopular with the military.

The whereabouts of both men were unknown Friday.

The unidentified coup leaders, calling themselves the Military Command, said in a statement they do not want to take power. They say they acted because of an alleged secret agreement that would allow Angolan forces to attack Guinea-Bissau's army.

The army is known for meddling in the West African country's political affairs. Renegade soldiers killed President Joao Bernardo Vieria in 2009.

The West African bloc ECOWAS and local African Union representative Sebastian Isata have condemned the soldiers' actions. The U.S. embassy in Senegal, which also covers Guinea-Bissau, urged the military to restore civilian leadership.

The embassy on Friday warned Americans in Guinea-Bissau to avoid the downtown area of the capital, Bissau. Witnesses say the capital was generally calm Friday, though soldiers patrolled the streets and local radio stations were off the air.

Guinea-Bissau's opposition — led by second-place finisher Kumba Yala — had called for a boycott of the April 29 presidential runoff and warned against campaigning. Yala was one of five candidates that claimed the first-round vote was rigged.

The candidates were vying to replace the late president, Malam Bacai Sanha, who died in January after a long illness.

Since winning independence from Portugal in 1974, Guinea-Bissau has struggled through a dictatorship, three coups and President Vieria's assassination. The country is also a conduit for traffickers shipping drugs to Europe.