At least 25 people have been killed and 170 injured after three bombs exploded during a procession by Shia Muslims in the Pakistani city of Lahore.
Lahore police chief Aslam Tareen told the BBC that at least two of the attacks had been suicide bombings.
Local TV footage of the first blast showed a small explosion in the crowd, followed by panic as people fled.
The capital of Punjab province has been the scene of sectarian violence between Sunni and Shia in recent months.
However, there had been a lull in such attacks in the past month, as floods devastated Pakistan.
Officials say the first explosion came shortly before nightfall on Wednesday, at the end of a procession by some 35,000 Shia to mark the death in the Seventh Century of the first Shia imam, Ali bin Abi Talib.
Footage of the moment shown on Geo television showed a small explosion amid a crowd of people near the Karbala Gamay Shah imambargah, followed by a large plume of smoke.
Minutes later, as hundreds of people fled, a suicide bomber blew himself up near an area where food was being prepared for the marchers to break the Ramadan fast, a senior police officer, Zulfiqar Hameed, told the Associated Press news agency.
A second suicide bomber then detonated his explosive belt at an intersection near the end of the procession, Mr Hameed added.
"The mourning process had just ended when I heard three deafening explosions after brief intervals," said Shahid Hussain, one of those who took part in the procession.
It is not known whether the first blast was a suicide bomb attack, but local government official Sajjad Bhutta told the AFP news agency that investigators had collected the bodies of three bombers.
At least 35 of the people were critically injured in the attacks.
Following the bombings, members of the public turned on police, attacking officers, their vehicles and nearby facilities.
Mr Pareen said that on the outskirts of the city at least one police station and one police truck had been set on fire. Other vehicles in the city were also torched.
Officers had fired tear gas in an attempt to control the crowds, he added.
Prime Minister Yousef Raza Gilani described the bombings as "cowardly acts of terrorism", and said that the perpetrators would be punished.
"Those elements playing with the lives of innocent people would not escape the law of the land," he said in a statement.