The opposition alliance led by Erdimi, Mahamat Nouri and Adbelwahid Aboud Makaye had crossed southern Chad from bases in Sudan. The government has accused Sudan of backing the opposition forces.
France, a former colonial power in the country, has sent 150 troops as a "precautionary measure" in the wake of the opposition alliance's advance on Ndjemena.
The troops arrived in the Chadian capital early on Friday to help "respond to the evolution of the situation" on the ground in Chad, Colonel Thierry Burkhard, French defence ministry, said.
An advance guard of EU peacekeepers, which was due to deploy on Friday, has been held back in light of the most recent clashes between government forces and opposition fighters.
"At the moment we don't want to blow this out of proportion, but yes, a flight of Irish troops yesterday and two flights today (Friday) have been postponed as a consequence of the increased instability in Chad," the spokesman said.
General Jean-Philippe Ganascia, head of the European EUFOR peacekeeping force in the country, said on Thursday that any opposition alliance advance would delay, but not divert, the mission.
EUFOR's mandate is to protect refugees from Sudan's war-torn Darfur region, which lies just over Chad's eastern border, as well as people displaced from the Central African Republic and from within Chad.
"I am not concerned [by the rebel manoeuvres] unless during their offensive they threaten or attack civilians, or the non-governmental organisations, or UN personnel," he said in Abeche.
He warned that if the opposition alliance forces confront the EU peacekeepers "believe me, I will face them down".