There has been a major battle in eastern Chad, with continuing heavy fighting, a rebel group says.
Chad's army had claimed victory against one rebel group
The Rally of Forces for Change (RFC) says government forces attacked them at dawn 150km north of the town of Abeche. No casualty figures were given.
The latest clashes come 24 hours after the rebels seized a number of army officers and vehicles.
President Idriss Deby is reportedly on the ground in eastern Chad commanding his troops.
His army is fighting on two separate fronts: to the south of the current battles with the RFC (led by the president's uncle, Timane Erdimi) at Biltine, they have also been engaging the better-equipped fighters of Mahamat Nouri's Union of Forces for Democracy and Development (UFDD).
The UN's refugee agency says it is concerned about the latest fighting and its impact on the camps in the region.
RFC, led by Timane Erdimi, president's uncle
UFDD, led by Mahamat Nouri
FUC, led by ex-Defence Minister Mahamat Nour Abdelkarim
A major battle with the UFDD at Abou Goulem a week ago left hundreds dead and the army said it had chased the remnants of the unit across the border.
The UN also warns that two other rebel groups - who along with the RFC and UFDD, signed a Libyan-brokered ceasefire a month ago - are also poised to re-enter combat.
Soldiers from recently-ousted Defence Minister Mahamat Nour Abdelkarim's United Front for Change (FUC), who had been integrating into the national army, are reportedly defecting en masse from at least two garrisons, at Adre and Guereda.
And negotiations with a fourth rebel group, the Chadian National Concord (CNT) have also broken down, the UN says, with the CNT forces poised to attack Daguessa from their bases inside Sudan.
The rebels accuse Mr Deby of being a "tyrant" and favouring members of his Zagawa community.
This bleak picture coincides with a prediction that the European Union peacekeeping force (Eufor) being put together for Chad "risks becoming engulfed in the region's conflicts".
A study by the Massachusetts Institute of Technology says Eufor would need 12,500 soldiers to be effective in ensuring security of the displaced civilians in the region.
The author, Bjorn Seibert, says the planned contingent is undermanned and under-equipped for its proposed task.
France will supply the bulk of the Eufor peacekeeping force
France is planning to contribute the bulk of the planned 3,500 troops - but the rebels have accused France of backing the government.
The timetable for Eufor's deployment, initially planned for January 2008, is already slipping because of difficulties in obtaining the attack helicopters needed.
Insiders now say it is unlikely to be operational before May 2008.
Some of the contributor nations have expressed their alarm at rebel statements saying the Eufor will be treated as an "occupying force" and targeted for attack.
1. RFC fighting between Biltine and Guereda
2. FUC defecting from Chadian army in Adre and Guereda
3. UFDD in heavy battles at Abou Goulem and at border with Sudan
4. CNT forces on Sudanese side of border near Daguessa