The Sudanese government arrested leading figures of the Sudan People's Liberation Movement (SPLM) during a protest outside the National Assembly in Khartoum on Monday, news services report.

The Sudan Tribune said those arrested included SPLM secretary-general Pagan Amum, his deputy, Yassir Arman, and a minister in Sudan's coalition government, Abbas Goma’a.

The SPLM is the ruling party in Southern Sudan, and the Tribune said the protest was held to protest against the failure of the government to pass legislation to reform the law ahead of next year's national election and the January 2011 referendum on independence for the south.

Police declared the protest illegal but Agence France-Presse reported that by mid-morning, "several hundred opposition protesters trailed by armed police were marching on the streets of Khartoum and Omdurman, waving placards and chanting 'We want our freedom.'"

The Tribune reported that police beat demonstrators and onlookers with batons as Arman was driven away chanting "freedom."

Speaking from a police station on a cellphone, Arman reportedly told Al Jazeera television news that the authorities had given permission for the protest. Al Jazeera said its crew was stopped from covering the protest.

The Tribune said the government ban on the protest was a reversal of its previous position, which was to allow people "any manifestation that is in accordance with the laws to express their opinion.”

Eyewitnesses told the news service that thousands of heavily-armed policemen took up positions on the streets of Khartoum on Monday morning. Amum was quoted as saying demonstrations would escalate if election reforms were not passed into law.