KHARTOUM/CAIRO (REUTERS) - A British journalist working for Bloomberg News in Sudan said on Wednesday that security agents had detained and beaten him for covering the country's biggest anti-government protest in years.

Sudan's information ministry could not be reached for comment, but a senior official in the ruling party condemned the security action as "unacceptable."

Mr Michael Gunn, 35, who said he had been working as a freelance reporter for Bloomberg News in Sudan, told Reuters that security agents detained him for covering a rally on June 29 where thousands demanded that President Omar Hassan al-Bashir resign.

"Plainclothes agents grabbed me and threw me with other Sudanese citizens in a van," Mr Gunn said. "They hit me several times, searched my bag and pulled my shirt over my head."

Agents then brought him to a building where he saw men dressed in police uniform.

"They interrogated me for three hours, slapped and threatened me," Mr Gunn said, adding that the agents later put him in a car and dropped him in a street.

He said he left Sudan a few days later.

"When a reporter is doing his job as he was and is attacked for no other reason, it's cause for concern," said Mr Ty Trippet, spokesman for Bloomberg News.

The New York-based Committee to Protect Journalists said: "Sudanese authorities assaulted and threatened an international journalist, with apparent impunity and with the effect of preventing the reporter from carrying out his duties."

Mr Rabie Abdelati, senior official in Bashir's National Congress Party, said he had asked the security services to investigate the incident. "This is an unacceptable behaviour of some individuals," he said. "I regret this."

Security officials were not available to comment. Critics say agents regularly hassle journalists and if there is a public outcry, blame the incident on officers allegedly acting on their own.

Earlier, the editor of the al-Youm al-Tali daily, a Khartoum-based newspaper respected for its independent stance, said it had been banned by the security apparatus.

"I got a phone call from the security services at noon informing me that we have to stop publishing and that they would start legal action against us," said Muzamil Abu al-Gassim. "They gave us no reason."

Al-Youm al-Tali and communist newspaper al-Midan, which was banned last month, are among a handful of newspapers that have dared print occasional criticism of the government. Most others carry mainly official statements and their front pages often look identical as security agents telephone editors to "coordinate" coverage plans, journalists say.