* Military rulers cancel agreements with opposition
* Opposition says to continue civil disobedience
* Calls for international inquiry into Monday's deaths
* Analysts see risk of violence escalating

Sudan's opposition on Tuesday rejected a plan by its military rulers to hold elections within nine months, a day after the worst bout of violence since Omar al-Bashir was ousted as president in April.

At least 35 people were killed on Monday when security forces stormed a protest camp outside the Defence Ministry in central Khartoum, said doctors linked to the opposition.

The Transitional Military Council (TMC) that has ruled since Bashir's overthrow then cancelled all agreements reached with the main opposition alliance.

Madani Abbas Madani, a leader of the Declaration of Freedom and Change Forces (DFCF) opposition alliance, said an open-ended civil disobedience campaign would continue to try to force the council from power.

‘What happened (on Monday) - the killing and injuring of protesters, the humiliation - was a systematic and planned attempt to impose repression on the Sudanese people,’ Madani told Reuters.

The main protest organizers, the Sudanese Professionals Association (SPA), called for an international committee to investigate the deaths in what it branded a ‘massacre’.

The mood in the capital Khartoum was very tense on Tuesday, with many roads barricaded by protesters, many shops shut and streets mostly empty. Security forces were trying to clear the barricades, a Reuters witness said.

Rapid Support Forces (RSF) vehicles were patrolling the streets in Omdurman, on the other side of the River Nile from Khartoum, and firing into the air.

Leaders of the protests that forced Bashir from power after three decades of authoritarian rule have demanded preparations for elections during a transitional period led by a civilian administration.

The military council has also been under both domestic and international pressure to hand over power to civilians. It had previously agreed to a three-year transition period with the DFCF.

‘We believe that the matter is now in the hands of the Sudanese people,’ said Khalid Omar Yousef, a DFCF leader. ‘This regime will fall, no matter what.’

RISK OF ESCALATION

The SPA rejected the establishment of a governmental committee to investigate Monday's deaths, spokesman Amjad Farid said, adding that the TMC was accused of targeting protesters.

Council spokesman Lieutenant General Shams El Din Kabbashi denied this charge and said security forces had pursued ‘unruly elements’ who fled to the protest site and caused chaos.

Sudan has been rocked by unrest since December, when anger over rising bread prices and cash shortages broke into sustained protests that culminated in the armed forces ousting Bashir.

But talks between a coalition of protesters and opposition parties ground to a halt amid deep differences over who will lead a transition to democracy that both sides had agreed will last for three years.

In a televised address early on Tuesday, TMC Head Lieutenant General Abdel Fattah al-Burhan said the opposition coalition was equally responsible for the delay in reaching a final agreement.

The council has decided to cancel all agreements with the protest groups and called for elections within nine months under regional and international supervision, he said.

‘Gaining legitimacy and a mandate does not come but through the ballot box,’ Burhan said, adding that a government would be formed immediately to run the country until elections are held.

Burhan said he regretted the violence and said it would be investigated.

The security forces' operation drew condemnation from Europe, the United States and the African Union.

The Democratic Alliance of Lawyers, part of the SPA, on Tuesday urged ‘some Arab countries’ not to interfere in Sudanese affairs and to drop their support for the TMC.

The alliance's comments appeared to be aimed at Saudi Arabia, the United Arab Emirates and Egypt, which analysts say are trying to consolidate their influence in Sudan following Bashir's overthrow.

The Soufan Group, a security and intelligence think-tank, said the violence could swiftly escalate.

‘There are clear parallels to some of the Arab Spring protests that eventually progressed to full-blown insurgencies, including Syria, where indiscriminate shelling of civilians by the military initially galvanized protest movements that helped launch a broader uprising,’ it said in an analysis.

‘There is a real risk that the situation could spiral into full-blown civil war, which would significantly affect the region, with spillover violence impacting the ongoing conflict in Libya.’

However, Hamid Eltgani Ali, a professor at the American University in Cairo, predicted that the protest movement would succeed in forcing the military to step down. There were two competing visions for Sudan's future, he told Reuters.

‘The vision of hate and division is led by the Janjaweed (militias) and military resisting to preserve their economic interests they enjoyed during Bashir's rule, while the vision of hope is led by professional associations and syndicates. They want a democratic, open Sudan with a strong developmental vision,’ Ali said.

Sudan has been on a US list of states that sponsor terrorism since 1993 that denies the country access to financial markets and strangles its economy.

Washington lifted a 20-year trade embargo against Sudan in 2017 and was in discussions to remove it from the sponsor of terrorism list when the military stepped in to depose Bashir.