On Wednesday, a powerful car bomb apparently exploded by a suicide attacker in a search line outside of Baghdad's convention center, an area in the heart of the city frequented by Americans and foreigners. A police official at the scene said only that there were Iraqi civilian and Iraqi National Guard casualties, but would not specify how many. July 14 is a national holiday commemorating the 1958 revolution that overturned the monarchy.

Insurgents killed a Bulgarian hostage in Iraq and vowed to kill a second Bulgarian within 24 hours, al-Jazeera television reported Tuesday.

The Arab satellite station said it had decided not to broadcast a videotape of the killing because it was too gruesome. But it showed footage of one of the Bulgarians kneeling before three masked men and wearing a blindfold and orange jumpsuit, a uniform typical of U.S. jails and associated around the world with images of Muslims detained by the United States at Guantanamo Bay, Cuba.

Bulgaria, which has contributed 470 troops to U.S.-led forces in Iraq, confirmed that one of the two truck drivers had been killed. "One of the Bulgarians has been executed," said Bulgarian government spokesman Dimitar Tsonev.

Bulgaria, which has said it will keep its troops in Iraq as long as they are needed, had urged the militants to release Georgi Lazov, 30, and Ivailo Kepov, 32, who disappeared June 27. There was no word on which man had been killed.

The Monotheism and Jihad Group, which had asserted responsibility for the beheading of an American and a South Korean in Iraq, threatened Thursday to kill the Bulgarians within 24 hours unless U.S.-led forces freed all Iraqi detainees. The U.S. military has branded the group's leader, Jordanian-born Abu Musab Zarqawi, its number one target in Iraq, saying he is behind much of the violence racking the country.

In a new hostage crisis, al-Jazeera said militants had set a 72-hour deadline to kill an Egyptian if the Saudi company he worked for did not pull out of Iraq.

On Wednesday, Philippine officials said they were coordinating to withdraw troops from Iraq following demands for a pullout from militants holding a Filipino hostage.

Confusion reigned over whether the Philippines intended to bring its troops home a month ahead of their scheduled Aug. 20 departure to save Angelo de la Cruz, 46, a truck driver threatened with death.

A Philippine Foreign Ministry statement said the number of troops in Iraq had dropped to 43 from 51, but did not say when the cut was made. A military spokesman said that no order to pull out had been received but that two transport planes were being prepared just in case.

The Reuters news agency contributed to this report.

Police in Manila clash with protesters urging the Philippines to withdraw its troops from Iraq to save the life of hostage Angelo de la Cruz. Officials said they were coordinating to withdraw troops, but did not say a pullout had been ordered.