The government has said that the rebel offensive in the provinces of Tibesti and Kanem was over
The Chadian army said on Monday it had killed 300 rebels in the north of the country at the weekend, adding that it had lost five of its soldiers.
A heavily armed rebel group had launched a raid from its rear base in Libya on April 11, the same day as Chad's presidential election that is expected to see the incumbent Idriss Deby Itno returned to power.
The raid by the Front for Change and Concord in Chad (FACT) has since resulted in "more than 300 rebels neutralized" and claimed the lives of five government troops, army spokesman General Azem Bermandoa Agouna told AFP.
Bermandoa said 36 soldiers had been wounded in fighting on Saturday and 150 rebels were taken prisoner, including three senior members.
The government has said that the rebel offensive in the provinces of Tibesti and Kanem was over.
Fighting resumed on Sunday afternoon, General Bermandoa said, adding however that calm had returned to the area.
FACT, for its part, said in a statement on Sunday that it had "liberated" the Kanem region that saw clashes on Saturday.
Bermandoa said 24 vehicles had been seized and that mopping-up operations were ongoing to "track down the last ones fleeing."
Tanks were deployed in the main roads of the Chadian capital N'Djamena, an AFP journalist reported.
The Tibesti mountains near the Libyan frontier frequently see fighting between rebels and the army, as well as in the northeast bordering Sudan. French airstrikes were needed to stop an incursion there in February 2019.
The Union of Resistance Forces (UFR), led by Deby's nephew Timan Erdimi, had entered Chad from Libya in columns of pick-up trucks.
The UFR said on Sunday that it supported FACT, but without saying whether its fighters took part in Saturday's clash.
The UFR was allied with Chadian rebels in 2008 when they launched a coup attempt, stopped at the gates of the presidential palace by French military intervention.
Deby assured re-election
FACT is based in Libya, where it has a non-aggression pact with Khalifa Haftar, a military strongman who controls much of the country's east.
It is mainly made up of the Saharan Goran people, while the UFR is majority Zaghawa, the president's ethnic group.
The US embassy in N'Djamena on Saturday ordered non-essential personnel to leave the country, warning of possible violence in the capital.
Britain also urged its nationals to leave the country.
But Chadian Foreign Minister Amine Abba Sidick appealed for calm, saying: "The situation is not worrying. The military situation is well under the control of the Chadian army."
Meanwhile, vote-counting was continuing from the April 11 election in which Deby is assured victory after sidelining his main rivals.
Deby, who has ruled the former French colony with an iron fist for 30 years, campaigned on security issues in the troubled region.
Preliminary results will not be announced until April 25.