The United States on Saturday ordered all non-essential personnel, including families of diplomats, out of Chad, as armed groups advanced towards the capital N'Djamena.
Chad's government said it had "destroyed" Libya-based "mercenaries" that crossed the border last Sunday during Chad's presidential election.
President Idriss Deby who ran for his sixth term is one of the continent's longest-serving heads of government, but his strong-arm, 30-year rule has prompted increasing opposition. On 8 April Human Rights Watch said "Chad's security forces have ruthlessly cracked down on protesters and the political opposition in the lead-up" to the elections, "harming Chadians' right to freely choose their elected representatives".
Also on Saturday the British government advised all its nationals to leave Chad as soon as possible, saying "armed rebel vehicles" had passed the town of Faya 777km (483 miles) from the capital. The French government advised its citizens not to travel outside the capital for any reason.
The armed group FACT - Front for Change and Concord in Chad - issued a statement saying France, which has intervened in the past to support the Deby government, is not its enemy.
The group assured Chad's people and international partners that it would provide peace and security. It is calling on Chad's military officers and rank and file to join the revolt.