NDJAMENA, April 1, 2008 (AFP) - Fighting broke out between rebel and government forces in eastern Chad Tuesday, nearly two months after a failed bid to oust President Idriss Deby Itno, rebels and the government said.

The clashes erupted around the town of Ade in hot, arid eastern territory bordering Sudan's Darfur region, said Ali Gadaye, spokesman for the main rebel group, the National Alliance (AN), led by General Mahamat Nouri.

'The fighting stopped at about 3:00 pm (1400 GMT)' around Ade, said Gadaye, reached by satellite telephone from Libreville. 'The clashes risk resuming in the coming days.'

A statement from Chad's defence ministry confirmed the fighting and claimed the rebel attack was authored by Sudan in violation of the March 13 peace pact made in Dakar -- the latest of many signed between the two neighbours.

The statement described the rebels as 'mercenaries' and said 'government forces pushed back the enemy, which is completely routed.'

Chadian Prime Minister Delway Kassire accused Sudanese President Omar al-Beshir of wanting to 'demolish Chad regardless of the cost,' in remarks before the diplomatic corps.

Charges of Sudanese involvement were rejected by both the Sudanese military and Gadaye, as Chadian rebels and government each blamed the other for the clashes.

'Government forces came, they attacked us, we attacked them back and we are now occupying Ade,' said a second rebel spokesman who asked not to be named.

Meanwhile, UN Secretary-General Ban Ki-moon expressed deep concern about the risk of insurgent strikes on Chadian territory.

'The secretary-general is deeply concerned by reports of continued movement of rebel groups across the Chadian/Sudanese border and by the possibility that these groups may launch attacks on Chadian territory,' Ban's office said in a statement.

An alliance of three rebel groups crossed the whole of southern Chad from the Sudan border area early this year and launched an assault on Ndjamena over the weekend of February 2-3.

They were driven out by Deby's troops with French military intelligence and reconnaissance support, after the head of state was holed up in his palace, an estimated 400 people were killed and thousands had fled across the border.

The rebels then withdrew to southeastern Chad. Their fractious alliance fell apart on tribal lines and reformed, headed by Nouri, who was last weekend joined by the Union of Forces for Change and Democracy (UFCD).

Ade lies 150 kilometres (95 miles) southeast of Abeche, the main town in eastern Chad, where the army and French troops permanently deployed in the former colony are based, along with a contingent in Ndjamena.

Abeche is also being turned into the headquarters of a 3,700-strong force called EUFOR Chad-CAR, in which peacekeeping troops from 14 European nations are currently deploying with a year-long UN mandate to protect Darfur refugees in Chad and the Central African Republic to the south.

The February rebel offensive on Ndjamena delayed EUFOR deployment, but these soldiers are due to be on the ground by the start of May's rainy season. They have no mandate to intervene in internal conflict unless attacked.

Deby and Sudan's President Omar al-Beshir last month in Senegal signed the sixth pact between the two countries and again agreed to prevent rebels from operating out of their territory. All previous such accords have been breached.

Chad on Tuesday urged mediators in the Dakar accord -- Senegal, Gabon, Congo and Libya -- to 'assume their responsibilities to end this aggression with its unforseeable consequences.'

The call coincided with the announcement of the mediators' first meeting, set for April 10, by the Gabonese foreign ministry.