Chadian rebels are reporting renewed fighting with government troops in eastern Chad.
Spokesmen for the rebel National Alliance say their forces shot down a government helicopter Thursday after coming under aerial attack.
The rebels say they are launching a new offensive toward the capital, N'djamena, with the intention of overthrowing President Idriss Deby.
The Chadian government has not confirmed the fighting but officials said a helicopter was forced to make a hard landing today in the eastern town of Abeche. There are no reported casualties from the incident.
The eastern-based rebels attacked the capital in February, besieging Mr. Deby in his palace.
The alliance of rebel groups has been trying for more than two years to overthrow president, who they denounce as autocratic and corrupt.
Chad accused neighboring Sudan of backing February's overthrow attempt. Sudan, in turn, accused Chad of backing an attack by Sudanese rebels on Khartoum in May.
Relations between the government have been hostile despite several peace agreements between Mr. Deby and Sudanese President Omar al-Bashir.
Some information for this report was provided by AFP and Reuters.
