Southern Sudanese leaders, human rights activists and political groups joined forces on Sunday to accuse Sudan's government of torturing suspects and making "arbitrary" arrests in a crackdown following a rebel attack on Khartoum.

Sudan's government dismissed the allegations as "absolutely not true" and "rubbish".

The new grouping - which included two prominent members of Sudan's coalition government - said an unknown number of Darfuris had been rounded up after the insurgent Justice and Equality Movement (JEM) raided the capital on May 10.

"We are saying the security forces should stop the arbitrary arrest of Darfuris," said Yasir Arman, of the Sudan People's Liberation Movement (SPLM), former southern rebels who formed a coalition government with the ruling northern National Congress Party after a 2005 peace deal.

"It is a violation of the constitution and it is damaging and harming the social fabric of our society. We also condemn in the strongest terms the torture of detainees, which is a grave violation of the constitution," Arman, the SPLM's deputy secretary general, told Reuters.

The new pressure group also included SLM-Minnawi - a former Darfur rebel faction which joined Sudan's coalition Government of National Unity after signing a peace deal in 2006.

SLM-Minnawi officials said a number of their own senior officers were arrested by armed Sudanese security agents at one of the group's Khartoum bases late Saturday.

A spokesman said agents fired into the air before they forced their way into the house at 11.30 p.m. (2130 GMT) on Saturday and started beating people.

'SERIOUS INCIDENT'

"This is a very serious incident," said Mohamed Basheer Abdalla, chief of staff to the movement's leader Minni Arcua Minnawi. "We have no idea why this happened. We still don't know exactly who was arrested. We think it was up to 10 senior officers."

Dr Mutrif Siddig, Under Secretary at Sudan's foreign ministry, said some "suspects" had been detained after the JEM attack, but dismissed allegations of mass arrests and torture.

"This is absolutely not true," he told Reuters. "There has been very strong direction from the leadership that Darfuris should not be held responsible for what JEM did, especially the Zaghawas."

Human rights activists have raised particular fears about members of the Zaghawa tribe, an ethnicity shared by both Khalil Ibrahim, JEM's leader, and Idriss Deby, the President of Chad, whom Sudan accuses of supporting the attack on Khartoum.

Amnesty International this week said it had the names of more than 150 mostly Darfuris arrested "apparently without charge" since JEM launched its unprecedented attack on Omdurman, a suburb of Khartoum.

Other foreign-based groups, including Human Rights Watch, have also raised fears about the arrests. But the newly formed 'National Committee for the Protection and Defence of Individuals and Groups Affected by 10 May Events' is the most prominent group to speak up from inside Sudan's borders.

In a statement, the group called for fair trials for all arrested.

Opposition Popular Congress Party leader Hassan al-Turabi, linked in the past to the JEM rebels who have a similar Islamist agenda, was briefly arrested on May 12. His supporters told Reuters security agents surrounded his compound for four hours on Friday before leaving.