Partial provisional results in Chad's April 11 election released Saturday show President Idriss Deby leading and appearing to be headed for another term in office, extending his three-decade rule.
Preliminary results are expected April 25.
Deby is viewed in Europe and the U.S. as a key ally in the fight against terrorism in West and Central Africa. Within the country, though, there have been signs of growing discontent over his handling of Chad's oil wealth.
Opposition leaders had called on supporters to boycott the vote.
In addition, a group of Libya-based rebels, the Front for Change and Concord in Chad, has been launching attacks. The group attacked a Chadian border post in the north on election day.
Chad's army said Saturday that it had "completely destroyed" the convoy of rebels that attacked the country.
The British government said that two of the rebel group's convoys were approaching the capital, N'Djamena, Saturday.
The U.S. Embassy in Chad issued a security alert Saturday, ordering nonessential staff to leave the country because of potential violence in the city.
Britain also told its citizens to leave the country as soon as possible.