BAGHDAD, Iraq - New online statements by purported militants threatened attacks against three U.S. allies - Poland, Japan and Bulgaria - if they don't pull their troops from Iraq, a day after a Filipino hostage was released because the Philippines bowed to insurgents' demands and withdrew its tiny contingent.

Meanwhile, the death toll of U.S. forces in Iraq since the start of the war in rose to 900 early Wednesday, when a roadside bomb exploded north of Baghdad, killing one U.S. 1st Infantry Division soldier.

Maj. Neal O'Brien of the 1st Infantry Division said the most recent soldier killed was on patrol in a Bradley fighting vehicle in Duluiyah, 45 miles north of Baghdad, when the bomb detonated shortly after midnight today.

On Tuesday, the military said that two U.S. Marines and two U.S. soldiers were killed in action in Anbar Province, a Sunni-dominated area west of Baghdad. The Marines were killed in separate incidents while conducting "security operations;" one soldier was killed Monday, and a second died Monday of wounds.

A count by The Associated Press put the number of American soldiers killed since the war began at 900. Counts of the number of U.S. service members killed in Iraq vary, with some already exceeding the 900 figure.

The new threats against Poland, Japan and Bulgaria were worrying signs that militants may be emboldened by their success against the Philippines. The United States and other coalition allies had criticized the government for agreeing to withdraw its 51-member contingent to save the life of truck driver Angelo dela Cruz.

The same group that kidnapped dela Cruz, the Khaled bin al-Waleed Corps, took aim at Japan.

"To the government of Japan: Do what the Philippines has done. By God, nobody will protect you and we are not going to tolerate anybody," said a statement signed by the group. "Lines of cars laden with explosives are awaiting you; we will not stop, God willing."

A Foreign Ministry official in Japan said Wednesday that Tokyo would not pull its 500 troops.

An online statement from a previously unknown group that identified itself as al-Qaida's European branch contained threats to carry out deadly attacks in Bulgaria and Poland if the two countries don't withdraw their troops from Iraq.

The group said Bulgaria and Poland will "pay the price" just like the United States and Spain did, referring to the Sept. 11, 2001, attacks in New York and Washington and deadly explosions on trains in Madrid in March.

"To the crusader Bulgarian government which is allying itself with the Americans and to the Bulgarian people we demand, for the last time, that you withdraw Bulgarian troops out of Iraq or we swear we will turn Bulgaria into pools of blood if you don't comply," said the statement.

Bulgarian President Georgi Parvanov said he won't pull out Bulgaria's 480-strong infantry battalion from Iraq.

The group's statement also had a warning to Polish Prime Minister Marek Belka: "Pull your troops out of Iraq or you will hear the sounds of explosions that will hit your country, at the time we choose."

The Polish Defense Ministry said last week that Poland would cut its troop levels from about 2,400 to between 1,000 and 1,500 next January.

Deputy Defense Minister Janusz Zemke said today that withdrawing troops from Iraq would be a "terrible mistake" that would only encourage terrorism.