At least 50 people were killed in co-ordinated multiple bomb attacks during a funeral in in Baghdad's Shia stronghold of Sadr City.
Police said a car bomb went off near a funeral tent, a suicide bomber driving a car then blew himself up, and a third explosion followed as police, ambulances and firefighters were arriving.
At least 30 people were killed when the bomber smashed his car into the tent before setting off its deadly payload. The explosion set several nearby cars on fire, sending a towering plume of thick black smoke over the city.
Distraught survivors were seen attacking policemen and firefighters who tried to move them away. Puddles of blood surrounded the tent.
The attack happened hours after insurgents launched a suicide attack on a police headquarters in the city of Beiji, killing seven policemen and wounding 21.
Police officials said four suicide bombers stormed a headquarters for police commandos. Guards killed one while the three others were able to set off their explosive belts inside the compound. Beiji, a centre for oil refining, is 250 kilometres north of Baghdad.
The police said that most of the members of the commando unit were not in the compound at the time as they were carrying out a security operation outside the city, otherwise the casualty figures would have been higher.
The incidents are the latest in a months-long surge of violence that is raising fears Iraq is slipping back toward the widespread sectarian killings of 2004-2008.
More than 4,000 people have been killed between April and August, UN figures show. Another 396 have been killed so far in September.
Saturday's violence comes as voters in the northern Kurdish autonomous region cast ballots in local elections for the Kurdistan Regional Government's 111-seat legislature. Iraqi Kurds are looking to bolster their autonomy while insulating their increasingly prosperous enclave from the growing violence roiling the rest of the country.
In other violence, gunmen shot and killed two prison guards after storming their houses in a village near the city of Mosul early yesterday. Also in Mosul, two soldiers were killed and four others were wounded when a roadside bomb struck their convoy. Mosul, northwest of Baghdad, is a former militant stronghold.
There was no immediate claim of responsibility for the attacks. Al-Qaeda's local franchise in Iraq frequently targets Shia civilians and security forces in an attempt to undermine public confidence in the Shia-led government in Baghdad.
Additional reporting by Associated Press