(Updates with Sudan denial, Solana defending EUFOR role)

By Finbarr O'Reilly

ABECHE, Chad, June 17 (Reuters) - Chad accused Sudan's army of attacking a town on its eastern border on Tuesday and blamed its neighbour for Chadian rebel raids which have disrupted international aid operations to help thousands of refugees.

Sudan's military denied the accusation, which again showed tensions flaring between the two oil-producing African states over their common border that runs along the violence-torn western Sudanese region of Darfur.

Rebels fighting to overthrow Chadian President Idriss Deby said they had pushed back a government counterattack around the town of Am-Zoer, 70 km (40 miles) north west of Abeche, the main hub of international aid operations in eastern Chad.

The anti-Deby rebel National Alliance said earlier Am-Zoer had fallen to its fighters on Tuesday, the latest in a series of hit-and-run attacks by fast-moving rebel columns of vehicles racing though the bush of east Chad's rugged borderlands.

The recent fighting has forced the United Nations refugee agency UNHCR to suspend its activities in eastern Chad, where a European Union military force (EUFOR) is deployed to protect nearly half a million civilians displaced by conflict.

A statement from Chad's government said Sudanese army ground troops supported by helicopters attacked the Chadian military garrison at Ade on their border on Tuesday.

"By openly intervening with its army and aircraft in Chadian territory, Khartoum is taking off the mask from its aggression against our country," the Chadian government said.

In Khartoum, a Sudanese army spokesman said the accusation had "no basis in truth". "This is a knee-jerk accusation by the Chadian government repeated each time they are attacked by the Chadian opposition groups," he told Reuters.

Last month, Sudan said Chad was behind a Darfuri rebel attack that reached the outskirts of Khartoum. Chad denied that.

There was no immediate clear independent confirmation of the action at Ade, a frontier post in Chad's eastern Ouaddai region.

But aid agencies based at Abeche said they had heard reports of fighting between Am-Zoer and Guereda north of Abeche, thought to be between rebels and government forces including Darfuri irregulars who support Chad's President Deby.

EU DEFENDS ROLE IN CHAD

The anti-Deby rebels say their ultimate objective is the Chadian capital N'Djamena, some 700 km (450 miles) to the west.

But in contrast to a major insurgent assault on the city in February, in which several hundred people were killed, there are fewer signs this time of a concerted rebel push to the capital.

Chad's latest accusation against Sudan followed a speech by President Deby late on Monday in which he denounced what he said was an "international plot" seeking to plunge his country back into civil war.

Both the United Nations Security Council and the African Union have condemned the attacks by the Chadian rebels. U.N. Secretary-General Ban Ki-moon called for dialogue.

Furious at the apparent ease of the rebel advance, Deby late on Monday sharply criticised the European Union military force deployed in eastern Chad, accusing it of "closing its eyes" to killings of civilians and refugees by the insurgents.

Deby questioned the use of the EUFOR contingent, which has a mandate to protect nearly half a million Sudanese refugees and displaced Chadian civilians sheltering at camps in the east.

Speaking in Paris, EU foreign policy chief Javier Solana defended EUFOR, saying it was abiding by its neutral mandate.

"I can tell you EUFOR is doing a fantastic job there," Solana told reporters, adding that Deby had made the criticism "in a difficult time".

In February, former colonial ruler France strongly backed Deby when he resisted the rebel assault then on the capital N'Djamena. Deby has ruled Chad, a minor oil producer, since seizing power in a 1990 revolt.

During a weekend visit to Ivory Coast, French Foreign Minister Bernard Kouchner said France "has not intervened and will not intervene" in the latest fighting in Chad.

France has warplanes and troops in Chad under a cooperation accord and French soldiers make up more than half of EUFOR. (For full Reuters Africa coverage and to have your say on the top issues, visit: http://africa.reuters.com/) (Additional reporting by Moumine Ngarmbassa in N'Djamena, Opheera McDoom in Khartoum and Brian Rohan in Paris; Writing by Pascal Fletcher)

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