BAGHDAD, Iraq (AP) _ Insurgents blasted a freight train west of Baghdad on Thursday and exploded a bomb near a convoy in a northern city, injuring a U.S. soldier, as international organizations continued their exodus from Iraq.

In Baghdad, police said a motorist was arrested after trying to throw a hand grenade into a police station on the edge the capital's ``green zone,'' the heavily guarded headquarters of the U.S. occupation.

Police said the man was from Fallujah, one of the centers of resistance to the occupation.

A top U.S. diplomat on Thursday blamed al-Qaida for recent attacks in Iraq. In Saddam Hussein's hometown of Tikrit, U.S. soldiers raided six houses after receiving tips that the inhabitants were helping establish a ``new terrorist network'' there, a military spokesman said. .

The freight train was carrying military supplies near Fallujah west of Baghdad, when an improvised bomb set four shipping containers ablaze. No casualties were reported, but the attack sparked a frenzy of looting by Iraqis who carried off computers, tents, bottled water and other supplies.

A soldier from the 2nd Brigade of the 101st Airborne Division was slightly wounded early Thursday when a bomb exploded near a U.S. convoy in the northern city of Mosul, the military said.

The United Nations said Wednesday it was temporarily pulling its remaining international staff out of Baghdad, joining other organizations in withdrawing after Monday's deadly suicide car bombing at the Baghdad headquarters of the Red Cross.

The International Committee of the Red Cross and Medecins Sans Frontieres, or Doctors Without Borders, said it, too, was pulling its workers out of Baghdad.

``We have asked our staff in Baghdad to come out temporarily for consultations with a team from headquarters on the future of our operations, in particular security arrangements that we would need to take to operate in Iraq,'' U.N. spokeswoman Marie Okabe said.

She said it was not an ``evacuation,'' and that staff in the north would remain.

Okabe declined to give more details, but about 60 U.N. staff members were believed to be in Iraq, including some 20 in Baghdad, after Secretary-General Kofi Annan ordered most others out in late September.

The United Nations scaled down its staff following the Aug. 19 truck bombing at its Baghdad headquarters that killed 23 people, including the top U.N. envoy to Iraq, Sergio Vieira de Mello, and a smaller blast near the U.N. offices last month.

The Red Cross said it would remain in Iraq but would scale back the number of international staff _ now numbering about 30 _ and increase security for those who stay. The agency has 600 Iraqi employees.

The Red Cross withdrawal came despite a personal appeal by Secretary of State Colin Powell to remain in Baghdad because ``if they are driven out, then the terrorists win.''

On Thursday U.S. Undersecretary of State John Bolton said al-Qaida was partly to blame for the recent surge in attacks.

``I think the attack on the Red Cross demonstrated to many Iraqis that they are being used by al-Qaida and other terrorist groups for purposes that have nothing to do with the well-being of the people of Iraq,'' he said in an interview with British Broadcasting Corp. radio.

U.S. forces are suffering an average of 33 attacks a day _ up from about 12 daily attacks in July. A total of 117 American soldiers have been killed in combat since May 1 _ when Bush declared an end to major fighting _ or slightly more than the 114 soldiers who died in invasion that began March 20.

The escalating violence has unnerved many of Baghdad's 5 million people. Many parents are not sending their children to school for fear of further bombings.

``Today most of my friends did not come to school,'' said 18-year-old Duha Khalid at the Al-Khalisa girl's high school, located near a police station. ``We heard rumors about big bombs that will go off at the start of next week.''

There also was an apparent assassination attempt Wednesday night against an aide to Iraq's most influential Shiite Muslim cleric, Grand Ayatollah Ali Hussein al-Sistani.

Sistani's office in the city of Najaf said they had no details on the attack on the cleric in the nearby city of Karbala and would not give his name. The Baghdad newspaper al Zaman identified him as Abdel Mehdi al Karbali.

In Baghdad, police commander Maj. Gen. Hassan al-Obeid announced measures to bolster security in the capital, including additional 24-hour checkpoints and special patrols around sensitive locations, according to coalition-run Iraqi television.

The Iraqi Governing Council, meanwhile, called on neighboring nations to crack down on infiltrators crossing into Iraq and provide Iraqi authorities with information about former regime figures who may be hiding on their soil.

The council ``requests Iraq's brotherly neighboring countries to adopt a clear stand concerning those criminal acts that target Iraqi citizens and their civilian and security establishments, and their political and religious dignitaries,'' a statement said.

``There are more than 300 terrorists arrested thus far who have (foreign) nationalities,'' said Mouwafak al-Rabii, a governing council member. ``We do our part to protect our borders and we hope our neighbors do their part''.

Separately, Mohammed al-Jibouri, head of the State Oil Marketing Organization, said bad weather has delayed Iraq's crude exports from its southern oil terminal for the past three days.

Iraq, which used to sell about 2 million barrels a day before the war, is now exporting around 1.2 million barrels a day from its offshore Basra oil terminal in the Gulf.

The country has so far failed to resume exports from its northern oil fields because of a series of explosions and fires in a pipeline linking the fields to the port of Ceyhan in Turkey.

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Eds: Associated Press correspondents Tarek Al-Issawi in Fallujah, Katarina Kratovac in Tikrit and Mariam Fam in Mosul contributed to this report.