Chad closed its border with Sudan overnight and cut off all economic ties with its neighbouring country amid accusations of aggression from Khartoum, news reports said Tuesday.
A Chadian diplomat accused Sudan of looking for excuses to launch an attack on Chadian territory in a report carried by Britain's BBC news channel.
Sudan cut off diplomatic ties with Chad on Sunday, accusing N'Djamena of supporting rebels in the crisis-torn western Sudanese province of Darfur, reported dpa.
Chad's troubled east, which is also dominated by rebel militias, borders on Darfur.
Relations between N'Djamena and Khartoum have been strained for some time.
Both accuse the other side of offering rebels asylum and of acting as supply bases.
When Chadian rebels advanced as far as the capital N'Djamena in February, President Idris Deby accused Sudan of supporting them.