Police have detained two men for allegedly sending mobile phone text messages about race riots under a law that allows them to be held without trial.

The men, in their 20s, were arrested by police in Johor, where acting police chief Mohamad Mokhtar Mohamad Shariff said they were held under the Internal Security Act.

"I wish to stress that security in the state is under control and that the SMS messages being circulated are purely rumours and malicious," he was quoted as saying by the Star newspaper.

Police have boosted their presence in the state by increasing patrols and deployed some 200 anti-riot police officers to ensure security, according to the New Straits Times.

Racial tension

Race relations have become an increasingly fraught issue in Malaysia, which has a Muslim majority but vaunts its multicultural status.

A series of court cases - notably on conversions from Islam - has called that status into question, while activists have been campaigning for greater religious freedoms in a nation where proselytizing by other faiths is banned.

Last November, text messages about rumours that ethnic Muslim Malays would be baptised as Christians sparked a large Muslim protest in the northern state of Perak.

It led to a government warning that the Internal Security Act could be used on anyone spreading texts which could cause instability.

The latest case comes as Malaysia marks tomorrow the 50th anniversary of its independence from Britain.