Government troops in Chad have clashed with rebels from the Rally of Forces for Change (RFC), reports say.
The Rally of Forces for Change (RFC) is led by Timan Erdimi
The RFC said its positions had been bombed by Chadian helicopters on Saturday, raising fears that a major ground battle could soon take place.
The RFC signed a peace deal with the government in October, as had another rebel group, the Union of Forces for Democracy and Development (UFDD).
The UFDD has already clashed with government troops further south.
Speaking to foreign diplomats on Saturday, Chadian Foreign Minister Ahmat Allami said RFC rebel forces led by Timan Erdimi had clashed with government forces around Kalait, some 210km (130 miles) north of Abeche.
A spokesman for the RFC, Id Moura Maide, told the AFP news agency that the fighting had begun when Chadian military helicopters attacked one of the group's bases in the area.
President Idriss Deby, who the rebels are trying to overthrow, is on the ground in eastern Chad commanding his troops.
The clashes follow days of fierce fighting east of Abeche between Chad's army and the UFDD, during which the government said several hundred rebels had died.
The UFDD said it had broken the ceasefire because the government failed to honour the peace agreement brokered by Libya in March.
Under the deal, the government and four Chadian rebel groups agreed to an immediate ceasefire, an amnesty for civil and military personnel and the release of all prisoners. The rebels were also granted the right to form political parties and to join the military and security forces.
But the BBC's Stephanie Hancock in Ndjamena says that after some of the heaviest fighting seen in the country in several years, the ceasefire is now effectively dead in the water.
On Friday, the UFDD also said it had declared war against the French-led 3,500-strong European Union peacekeeping force which is due to be deployed in Chad in January to protect refugees from Sudan's Darfur region.
The rebels accused French military planes of flying over their positions and passing intelligence to the government during last week's fighting. French President Nicolas Sarkozy has insisted the declaration would not jeopardise the EU mission.
The latest fighting began as President Deby sacked his defence minister, Mahamat Nour.
A former leader of the United Front for Change (Fuc) rebel coalition, Mr Nour was appointed defence minister in March after agreeing to disarm his fighters and arrange for them to be assimilated into the Chadian army.
However, correspondents say this never really happened and last week the authorities said they suspected the fighters had instead taken up arms against the government again.
Officials say Mr Nour has taken refuge in the Libyan embassy in the Chad's capital, Ndjamena.