Chadian government troops clashed with rebel forces near Ndjamena, with both sides claiming victory in a battle that could eventually decide control of the capital Ndjamena.
Chad's military general staff said in a statement the army had engaged a large group of rebels at Massaguet about 50 km northeast of the capital and "entirely destroyed this column after 40 minutes of fighting".
"The Massaguet battle was very violent. The army did not succeed in pushing forward," a Chadian military source, loyal to President Idriss Deby, told AFP yesterday.
Rebel leader Timan Erdimi insisted his side had won the day and vowed the next clash would be in Ndjamena itself.
"We completely smashed them, but Deby was able to escape. Now we are between Massaguet and Ndjamena. We are coming to Ndjamena," Erdimi said by satellite phone.
Erdimi joined forces with fellow rebel leaders Mahamat Nouri and Adbelwahid Aboud Makaye in mid-December after a previous peace pact with President Deby fell apart.
An Ndjamena military source said President Deby had been at the front but had regained the capital.
As the fighting continued, the UN evacuated all "non-essential" staff from the Chadian capital to Cameroon. Around 160 non-essential personnel were evacuated for security reasons, said a Geneva-based spokeswoman for the UN refugee agency (UNHCR).
France meanwhile flew a combat unit of 126 extra troops into Chad to join the 1,100 permanently posted there.
But Air France said all access to Ndjamena airport had been blocked, preventing its scheduled flights from landing.