Main Baghdad streets were closed off with concrete blocks Thursday, and soldiers at roadblocks searched pilgrims as they entered roads leading to the shrine. A senior Defense Ministry officer said motorcycles had been banned to reduce the risk that one might slip a bomb past a checkpoint, and he said at least 30,000 soldiers and police were on the streets. He spoke on condition of anonymity to discuss the measures.

Authorities on Thursday raised the death toll to 72 and said the 22 explosions in seven cities and towns on Wednesday also wounded more than 270 people, according to two officials from the health and interior ministries. The officials spoke on condition of anonymity because they were not authorized to talk to the media.

The attacks around the country came amid political tension over power-sharing. Iraq's Sunnis and Kurds accuse the Shiite prime minister, Nouri al-Maliki, of consolidating power in his own hands.