At least 72 people have been killed in bomb attacks targeting Shia Muslims in southern Iraq and the capital Baghdad.
Officials said 45 pilgrims died in a suicide attack in Nasiriya and 27 people died in Shia areas of Baghdad.
The attacks were the deadliest since the last US soldiers pulled out of Iraq on 18 December.
Sectarian tensions have risen since the US pullout and since an arrest warrant was issued for Sunni Vice-President Tariq al-Hashemi.
The BBC's Rafid Jabboori in Baghdad says Iraq is going through a severe political crisis and the situation in the country is tense.