ATLANTA (NYT)- A car bomb killed at least four Iraqi national guardsmen Tuesday in a city north of Baghdad.

In South America the same day, rebels in Colombia killed nine police officers by blowing up a parked car about 160 miles outside the capital, Bogota.

Those explosions, on opposite sides of the globe, underscored the inexpensive lethality and worldwide appeal of the car bomb, a weapon of choice for terrorists that is easy to obtain and hard to stop.

Car and truck bombs gained currency in the 1980s and have since killed people in places as far apart as Argentina, the Russian region of Chechnya, Colombia, Greece, Israel, Kenya, Spain, Sri Lanka and Britain. Truck bombings killed six people at the World Trade Center in New York in 1993 and 168 at the Oklahoma City federal building in 1995.

This week, authorities in the United States warned of a possible car- or truck-bomb attack on the New York Stock Exchange and the World Bank and International Monetary Fund buildings in Washington.

Heavily armed police kept watch at the buildings Tuesday. Police banned parking in some places, closed roads and inspected vehicles. Yet preventing car and truck bombs is nearly impossible, said Vincent Cannistraro, chief of counterterrorism at the CIA until 1991.

"There is no absolute defense," he said.

The use of vehicles packed with bombs dates at least to the struggle for Israeli nationhood.

On July 22, 1946, a group led by future Israeli Prime Minister Menachem Begin detonated a truck bomb at the King David Hotel in Jerusalem, which housed British military personnel. The blast killed 92 people.

Car and truck bombings followed in the next few decades but became more common after militant Islamists used them in Lebanon in 1983.

In April of that year, a van carrying 2,000 pounds of explosives blew up the U.S. Embassy, killing 63 people. Then, on Oct. 23, 1983, a suicide bomber in a truck laden with explosives smashed into a four-story building housing American servicemen in Beirut. The attack killed 241 Marines.

That assault, and another explosion that killed French troops in the city, emboldened terrorists because the United States and France subsequently withdrew their troops from Lebanon, Cannistraro said.

"It was effective," he said. "It had the result of driving the Americans and French out of Lebanon."

Yonah Alexander, director of the International Center for Terrorism Studies in Washington, said terrorists use car and truck bombs because they can buy the ingredients cheaply on the open market.

He said most car bombs contain ammonium nitrate, a common fertilizer, and fuel oil, though sophisticated versions include military explosives. He said terrorists have no trouble learning how to manufacture car bombs.

"Just turn on the Internet," he said. "It's a weapon of choice because it is inexpensive and you don't have to be a rocket scientist to make one."

Elsewhere in Iraq Tuesday, insurgents killed a police chief in Baghdad and a patrolman in Mosul. And a roadside bomb killed two U.S. soldiers in the Iraqi capital while two Marines died of wounds received Monday in fighting in Anbar province, a volatile Sunni-dominated region west of Baghdad.

A third Marine was killed Tuesday after suffering a "nonhostile" gunshot wound, the military said. A U.S. soldier was killed Tuesday in a vehicle accident in Baghdad, the military said.

In other violence, a roadside bomb attack early Tuesday killed Col. Mouyad Mohammed Bashar, chief of al-Mamoun police station in Baghdad, along with another officer, officials said. A third officer was wounded.

Gunmen in the northern city of Mosul opened fire on a police station, killing one officer and injuring two others before fleeing, police chief Izzat Ibrahim said.

Editor's note: The Associated Press contributed to this article.