Sudan’s main opposition group says security forces raided its office and blocked a new conference on the eve of mass protests against military rule.

Security forces have been patrolling parts of the capital, Khartoum, ahead Sunday’s planned protests.

The Sudanese Professionals Association (SPA) called for a “million-strong” march on Sunday to push the military to hand control to civilians.

But there are no reports so far of huge protests in Khartoum.

• The warlord who may control Sudan’s future
• Instagram ‘scammers’ exploit support for protesters
• Profile: Sudan’s Omar al-Bashir

The military overthrew President Omar al-Bashir in April following a popular uprising against his rule.

He seized power in a coup on 30 June 1989.

The SPA had organised a media briefing on Saturday evening to unveil plans for the rally, which would be the first mass demonstration since dozens were killed when the military opened fire on pro-democracy protesters on 3 June.

Protest leader Ahmed al-Rabie told AFP news agency that the paramilitary Rapid Support Forces (RSF) had broken up the media briefing.

“Before we could start the press conference, three vehicles from RSF, full of armed men, came to our building and told us not to hold the press conference,” he said.

Everyone in the building was ordered to leave, Mr al-Rabie said.

He told Reuters news agency that the raid was “a violation of liberties that is even worse than the regime of the former president”.

• Sudan’s violent political crisis explained
• The art fuelling Sudan’s revolution

The military said it would hold the opposition responsible for any violence or loss of life in the protests.

Gen Mohamed Hamdan Dagalo, also known as Hemeti, warned of “vandals” and a “concealed agenda” that might take advantage of the demonstrations.

Shops were shut on Sunday in areas of the capital where protests were expected, AFP reports.

Talks between the Transitional Military Council (TMC) and the opposition collapsed after 3 June and have not resumed despite mediation by the African Union (AU) and Ethiopian Prime Minister Abiy Ahmed.

On Friday, the SPA said two leading members of the opposition had been detained and urged “the international community to demand their immediate release”.