Rebels in Chad say they have seized a strategically important town in the central region of Batha, about 400km (248 miles) from the capital, Ndjamena.
Rebels said a coalition of groups had launched the attack
A spokesman for several rebel groups who have joined forces said Oum Hadjer had been captured on Wednesday.
Army patrols have reportedly been increased in N'Djamena in case the rebels try to move on the capital.
A European Union peace force is preparing to deploy to eastern Chad in the next few weeks.
The 3,700-strong contingent will aim to protect refugees from Sudan's Darfur region and people displaced by internal fighting.
The rebels want to drive President Idriss Deby from power. Nearly two years ago a group entered N'Djamena before they were repelled.
The Chadian military said a convoy of rebel forces had been sighted in the area around Oum Hadjer, but that there was conflicting information about its movements.
The AFP news agency quotes military sources as saying that government troops have been mobilised to intercept a convoy of 300 rebel vehicles that are speeding towards the capital.
"We are moving towards N'Djamena," rebel spokesman Abderaman Koulamallah confirmed to AFP.
Meanwhile, army units have stepped up patrols on the streets of the capital, Reuters news agency says.
France's embassy has closed the French school in the city, French radio reports.
This comes after Chadian aircraft bombed rebel positions in the east near the border with Sudan on Tuesday.
The peacekeeping force - known as Eufor Chad/CAR - to be deployed in Chad and the Central African Republic - was given final approval on Monday and will mainly contain French troops.
France already has 1,100 soldiers in Chad under a 1986 agreement to guarantee "territorial integrity", but rebel groups believe the French helped thwart the attempted N'Djamena attack in 2006.
Rebels maintain the Eufor Chad/CAR will not be neutral.
Late last year, the main rebel group, the Union of Forces for Democracy and Development (UFDD), declared a "state of war" against French and other foreign forces because it said they were "bringing diplomatic, strategic and logistical aid" to the president.