The Defence Forces say it will be Wednesday at the earliest before Irish Army rangers can be deployed to Chad.
Their departure was delayed last night as the security situation there worsened.
Chadian government troops clashed with rebel forces near N’Djamena today, with both sides claiming victory in a battle that could eventually decide control of the capital.
Chad's military general staff said the army had engaged a large group of rebels at Massaguet about 50km northeast of the capital and ‘entirely destroyed this column after 40 minutes of fighting’.
Rebel leader Timan Erdimi insisted his side had won the day and vowed the next clash would be in N’Djamena itself.
‘We completely smashed them,’ he said. ‘Now we are between Massaguet and N’Djamena. We are coming to N’Djamena. I think we will be there tonight or tomorrow morning.’
As the fighting continued, the UN evacuated about 160 non-essential staff from the Chadian capital to Cameroon.
France meanwhile flew a combat unit of 126 extra troops into Chad to join the 1,100 permanently posted there.
The capital itself was practically deserted this afternoon, with a large military presence on the streets and helicopters flying overhead.
Military chiefs in Dublin and Paris have been reviewing the deteriorating situation in Chad.
The airport in the capital remains closed to civilian aircraft.
This afternoon, the Defence Forces said a decision on the deployment of the rangers would be taken over the next 72 hours.
Contingency plans are in place to deploy at the earliest opportunity but that would not be before Wednesday.
The eight Irish soldiers already in Chad are safe and well.
A cargo plane packed with military equipment at Dublin airport will now have to be unloaded.
However, the main deployment of 400 troops in the coming months is not expected to be held up any further.
The setting up to the EU peace mission in Chad has been dogged by delays. It was initially hoped that Irish troops would be joining the 3,700-strong peace force in early December.
