Foreign Minister Mustafa Osman Ismail said the agreement had not been renewed because Uganda had not given a time limit for their presence or specified where they would be operating.

We have reached a firm decision that we will not co-operate with the LRA

Mustafa Osman Ismail, Sudan Foreign Minister

The Ugandan army started "Operation Iron Fist" in March, after being authorised to enter Sudan to hunt LRA fighters.

Previously, Sudan had backed the LRA, while Ugandan had supported Sudan's SPLA rebels.

The BBC's Alfred Taban in Khartoum says that Ugandan soldiers are now illegally on Sudanese territory.

But Mr Ismail said that the decision would not hurt relations with Uganda because Sudan would not renew its backing for the rebels.

"We have reached a firm decision that we will not co-operate with the LRA," he told parliament.

But analysts say the decision will not go down well in Kampala.

Intensified

Meanwhile, the army has said that it has killed 28 LRA fighters and lost four soldiers during clashes in northern Uganda on Monday night, according to the French news agency, AFP.

The LRA have been fighting the government of President Yoweri Museveni for 14 years, demanding that Uganda be ruled according to the Biblical Ten Commandments.

Thousands of civilians have been abducted

But they have kidnapped thousands of children for use as fighters or sex slaves.

Operation Iron Fist has not been an unqualified success, despite repeated army claims to be on the verge of wiping out the rebels.

The LRA has fled its bases in Sudan and entered northern Uganda, where they have intensified their attacks.

Last month, the Ugandan army ordered 100,000 civilians in the north to leave their homes and move closer to camps protected by the military.

Army spokesman Shaban Bantariza told the BBC's Focus on Africa programme that the move was being made to prevent civilians getting caught in the crossfire as the army tracks the rebels down.