Allam-Mi told Reuters: "The Sudanese air force began yesterday to fly over the positions of the Chadian army. I summoned the Sudanese ambassador in Chad this morning to raise a strong protest and I said that Chad would take all the necessary measures."
 
Chad also accused Khartoum of supporting rebels who are fighting a low intensity war in eastern Chad to oust Idriss Deby, the Chadian president.
 
Counter-claim
 
Sudan has, however, denied the claims and said that troops from Chad had in fact crossed into Sudan.
 
But the Chadian minister rejected Sudan's accusations, calling them propaganda. Allam-Mi said: "This is a pretext to continue to attack our country.
 
Sudan is reassembling and rearming its mercenaries, as the attack against Ounianga Kebir demonstrates."
 
The anti-Deby rebel Union of Forces for Democracy and Development (UFDD) occupied the remote northeastern town of Ounianga Kebir early on Saturday morning.
 
Instability
 
Violence in the east of oil-producing Chad has been fuelled by instability and ethnic killings spreading across the border from the neighbouring Darfur region of Sudan.
 
The latest foray by the rebels appeared to be a hit-and-run raid typical of their long-running insurgency.
 
A rebellion and related conflict in Darfur has killed some 200,000 people since 2003.
 
Deby, a former fighter pilot, seized power in a 1990 uprising in eastern Chad and was re-elected to a fresh term in May in elections boycotted by the opposition.