Sudan's powerful intelligence service on Thursday said it had disrupted a "plot" to disturb the country's security, as a witness saw tanks moving in the streets of the capital, AFP reports.

"The security and intelligence service early today stopped a plot to disturb security," the Sudanese Media Centre, which is close to the security apparatus, said in a brief news alert which gave no further details.

A witness told AFP that he saw troops moving at about the same time.

"About 2:00 am (2300 GMT) while passing Obeid Khatim Street I saw some tanks and vehicles with military equipment and soldiers coming from a southerly direction and heading downtown," said the witness, who asked for anonymity.

Obeid Khatim Street is a wide thoroughfare running alongside Khartoum's military and civilian airports, leading into the downtown area where government buildings are located.

The report of the "plot" comes as concern grows over delays in implementing security and oil deals which the leaders of Sudan and South Sudan hailed in September as ending conflict, after they fought along their undemarcated border in March and April.

Sudan's army on Wednesday confirmed it attacked an area near the South Sudanese border where Darfur rebels had set up a compound, but South Sudan said bombs landed on its territory, killing five people.

"We attacked Al-Regaibat which is 40 kilometres (25 miles) north of the international border with South Sudan and 10 kilometres north of Samaha," army spokesman Sawarmi Khaled Saad said in a written statement.

Saad alleged that the rebels must have had "great support" from South Sudan, an accusation which goes to the heart of tensions between the two nations.

"There are five casualties, civilians: Two women, one man and two children," South Sudan's army spokesman Philip Aguer told AFP.

He said the casualties came on Tuesday when bombs fell in Kiir Adem, an area near Samaha and claimed by South Sudan.

"It's not a disputed area. It's near to the border", he said, accusing Sudan of more air raids even further south on Wednesday.

But Sudan's army spokesman insisted that "we conducted our battle deep inside Sudan."

Earlier Wednesday the Justice and Equality Movement (JEM) rebels from Darfur accused the government of bombing around the disputed border region, after the army had threatened to use force.

JEM is part of an alliance of ethnic-minority Sudanese insurgents seeking to overthrow the Arab-dominated Khartoum regime.

"Yesterday and the day before yesterday there was intensive aerial bombardment around the Samaha area," said Gibril Adam Bilal, JEM's spokesman.

He said the bombs landed in civilian areas and did not hit rebel positions.

On Monday, army spokesman Saad said rebels had built a compound, set up a checkpoint and were flying their flag in the Al-Regaibat area, at the Bahr al-Arab River.

Sudan and South Sudan dispute the area, which Sudan considers to be part of East Darfur state.

The Samaha region is one of five areas contested by Khartoum and the South's government in Juba.

They have not been able to resolve the disagreement despite African Union (AU) mediation which led to the September deals that included a demilitarised border buffer zone designed to cut support for insurgencies in Sudan.

Sudan has long accused South Sudan of working with the JEM, a charge denied by the South. But suspected JEM fighters were seen alongside South Sudanese troops during border fighting between Sudan and South Sudan in April.

The two nations have not been able to agree on practical steps to implement the September pacts, the AU said on November 10, urging "full and timely implementation".

On Monday the US State Department spokeswoman, Victoria Nuland, called on Sudan and South Sudan to meet again and recommit themselves to the September 27 accords.