N'Djamena: Chad accused Sudan of backing a new rebel advance, saying the move came even as another African country was trying to mediate between the neighbors.

According to a Chad government statement made on Thursday, Sudan launched ''several heavily armed columns'' against Chad a day earlier.

The Chadian government called the fighters ''mercenaries,'' - its term for Chadian rebels it accuses Sudan of backing.

Talks scheduled for Wednesday in Senegal between Chad and Sudan were delayed after Sudanese leader Omar al-Bashir failed to show up.