Pakistani President Pervez Musharraf has condemned a suicide bombing that killed 20 people at a Muslim shrine in Islamabad as a heinous act of terrorism. No group has claimed responsibility for Friday's bombing. A spokesman for U.N. Secretary General Kofi Annan urged Pakistani authorities to spare no effort in bringing those responsible to justice. The attack occurred Friday at the Bari Imam Shrine, where thousands of Shi'ite and Sunni Muslims were gathered for a festival honoring a Muslim saint. Some witnesses told a Pakistani newspaper that a young man casually kneeled down among the worshippers and blew himself up. The shrine is close to Islamabad's main government buildings and a number of embassies.