A suicide bomber blew himself up in a Shiite mosque during Maghreb (evening) prayers in the city of Rawalpindi near here yesterday, injuring three worshippers, police said.

"The attacker entered the mosque at prayer time," Brigadier Javed Iqbal Cheema of the Interior Ministry's Crisis Management Cell said. "There were not many people inside and he detonated his explosives prematurely.

"There were only three very minor casualties who were released after first aid."

Around 40 people were attending the prayers when the man detonated a low-intensity bomb strapped onto his body, killing himself, a police official said.

Three worshippers sustained minor injuries in the bombing, the first incident of violence since the Islamic month of Muharram marked by religious gatherings and processions by Shiite community started on February 22.

Police have made special security arrangements in cities and towns across the country for the annual commemoration of the martyrdom of Imam Hussain, grandson of Prophet Mohammed (PBUH). Troops have also been placed on alert in several sensitive areas.

The religious ceremonies will culminate on the 10th Muharram next week. The government has declared March 1 and 2 as public holidays.

Government officials said security had been further strengthened throughout the country following the Rawalpindi incident.

The country has a history of sectarian bloodshed blamed on religious extremists. President Pervez Musharraf has frequently vowed to root out sectarianism from the society and banned several extremist outfits.

The Civil Aviation Authority said airports had been put on their highest state of alert and security checks of passengers stepped up.

"Airports have been put on red alert since Thursday night because of Muharram and the situation in the country," said a spokesman, who declined to detail any specific threat.

Cheema said police were working to identify the mosque attacker, adding: "It looks like a sectarian attack."

The body of the attacker was intact but charred by the blast. He appeared to have disguised himself in mourning black.

Earlier this month, the government issued an order banning more than 300 hardline clerics from leaving their home districts to prevent them inciting violence during Muharram.

Last July, a suicide attack on a Shiite mosque in the southwestern city of Quetta killed more than 50 people.

Abdul Jalil Naqvi, a Shiite leader, said the attack in Rawalpindi, which adjoins the Pakistani capital Islamabad, was "part of the religious terrorism that has been going on for the last few years".

He called on the government to provide additional security over Muharram.