A suspected suicide bomber killed at least 13 people and wounded dozens more in the Pakistani city of Lahore on Monday.
The blast, outside the Punjab regional assembly building, targeted a rally by chemists and pharmaceutical manufacturers. They had been protesting against a new government law.
Some reports put the death toll nearer 20, with at least six police, including two senior officers, said to be among those killed.
Counter-terrorism officials had warned about a possible terrorist attack in Lahore, according to Pakistani media reports.
Jamaat-ur-Ahrar, a faction of the Pakistani Taliban, said it was behind the attack, declaring the start of a new campaign.
The same group also claimed responsibility for a bombing at a public park in Lahore last March targeting Christians celebrating Easter. That attack killed more than 70 people.