A suicide attack in southern Iraq has killed at least 53 people.

Authorities say the attack Saturday on a group of Shi'ite pilgrims near the city of Basra has left at least 100 people wounded. The blast struck near a police checkpoint on the route to a Shi'ite shrine.

The attack took place as many Shi'ites journeyed to the shrine to observe the end of an annual period of mourning. Security is high due to a series of attacks on Shi'ites in recent weeks.

Tensions between Shi'ite and Sunni Muslims in Iraq are high, especially since the withdrawal of U.S. troops from the country last year.

Under the regime of executed dictator Saddam Hussein, the government was dominated by Sunni Muslims.

Iraq's present government, headed by Shi'ite Prime Minister Nouri al-Maliki, is dominated by Shi'ites. But it includes Sunnis and Kurds in a fragile power-sharing government that is rife with sectarian tensions.

More than 100 people have been killed in a spate of attacks on Shi'ites since the government issued an arrest warrant for Sunni Vice President Tariq al-Hashemi last month. He is charged with operating a death squad.

Hashemi has denied the charges. He fled to Iraq's autonomous Kurdish region to avoid detention.