BAQUBA, Iraq - A suicide bomber on Sunday struck a crowd of Shiite pilgrims in Baquba, the capital of Iraq's eastern province of Diyala, killing three people and wounding four others, a provincial police source said.

The attack took place in the morning when a suicide bomber blew up his explosive vest at a procession of Shiite pilgrims in al- Gatoon area in western Baquba, some 65 km northeast of Baghdad, a source from Diyala's operations command told Xinhua on condition of anonymity.

Iraqi security forces sealed off the scene as ambulances evacuated the victims to the city hospitals, the source said.

Shiites in Iraq are marking the 10-day annual Ashura mourning rite, the holiest of the Shiite religious calendar, which marks the death in 680 AD of Imam Hussein, grandson of the Prophet Mohammed.

The Shiite mourners usually gather in processions in their towns and cities before they move on foot or buses to the holy shrines in Karbala, some 110 km south of Baghdad.

Iraqi and US officials frequently blamed al-Qaida militant group and some insurgent groups for carrying out attacks against Shiite pilgrims who perform communal rituals, killing and wounding hundreds of them in attempts to provoke sectarian strife in the violence-shattered country.

Diyala province, which stretches from the eastern edges of Baghdad to the Iranian border east of the country, has long been a stronghold for al-Qaida militants and other insurgent groups since the US - led invasion of Iraq in 2003 despite repeated US and Iraqi military operations against them.