Heavily-armed rebels have entered the east of the country from Sudan, Chad's government is saying.An announcement on national radio reported that "mercenaries crossed the border in the area of Moudeina", north of the border town of Ade.
A rebel attempt to overthrow President Idriss Deby's government was thwarted last month.
Mr Deby is due to sign a non-aggression pact in the next few hours with President Omar al-Bashir of Sudan.
There is no independent confirmation of the incursion, but it was reportedly denied by the leader of the main Chadian rebel alliance, Mahamat Nouri.
According to the AFP news agency, General Nouri accused Chad's government of looking for "an excuse" not to sign the peace agreement with Sudan.
"There is no fresh offensive", it reported him as saying. "Nothing in particular is going on."
Accusations
Chad has accused Sudan of supporting Chadian rebels.
These charges are denied by Khartoum, which in turn accuses Chad of backing rebels in Sudan's Darfur region.
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