At least 19 people, mostly policemen, were killed and more than 70 were injured in a suicide bombing near Pakistan's Red Mosque, hospital and administration officials said Monday.
The attack on Sunday targeted a crowd of policemen guarding a rally by thousands of hardline Islamists in the capital to mark the first anniversary of a bloody raid on the mosque.
Fourteen policemen and five civilians were killed, while 73 other people were wounded, according to a tally of figures given to AFP from officials at the city's two main hospitals and in the Islamabad administration.
Prime Minister Yousaf Raza Gilani visited injured police officials at the Pakistan Institute of Medical Sciences hospital just before leaving for Malaysia to attend the D8 conference of developing countries.
"I pay tribute to the policemen. They did not care for their lives and protected the people attending the convention," Gilani told reporters.
"What has happened was against humanity and has brought Pakistan a bad name in the entire world."
Gilani said that it was a "cowardly act" and the people behind it would not escape punishment.