Chad's government has accused the Sudanese military of bombing two locations in the east of the country which borders Sudan's Darfur region.
Violence in the east has forced 120,000 Chadians from their homes
It said Sudan's air force was carrying out systematic bombing operations.
There is no clear information on casualties, but unconfirmed reports say two Chadian aid workers were wounded.
A BBC correspondent in Chad says relations between the neighbours have been strained for months despite a series of peace deals.
There has been no official comment from Sudan.
In a statement released on Thursday evening, Chad's government claimed two Sudanese planes bombed locations near the towns of Tenay and Bihi.
It is not clear who was the target of Thursday's alleged air attack but Darfur rebels hostile to the Khartoum government are known to operate in this area.
The BBC's Stephanie Hancock in the Chadian capital, N'Djamena, says this is not the first time that Chad has accused Sudan of bombing its territory.
But while previous allegations have been difficult to substantiate, sources in eastern Chad suggest that some sort of bombardment did indeed take place, she says.
There are also reports that Sudanese Antonov planes were seen in the region.
Our correspondent says this latest development will do nothing to ease the tension between the two countries.
The Chadian government has accused Sudan of backing rebels fighting President Idriss Deby - a charge Sudan denies - while Chad denies Sudanese claims that it supports black African rebels in Darfur.
The UN has approved funding for an 11,000-strong force to be sent to stabilise the lawless east, although Chad says it only wants a police operation, not a military one.
The conflict in Darfur has spilled over the border forcing some 120,000 Chadians to join more than 200,000 Sudanese refugees in displacement camps along the border.