A wealthy Syrian arms dealer previously accused of arming militants from Iraq to Somalia has been arrested in Spain on charges he plotted to supply millions of dollars worth of weapons to Colombian rebels, U.S. officials said Friday.

The arrest followed an international sting operation in which undercover agents with the Drug Enforcement Administration convinced Monzer al-Kassar that they wanted to buy surface-to-air missile systems, rocket-propelled grenade launchers, thousands of machine guns and millions of rounds of ammunition for the Revolutionary Armed Forces of Colombia, a rebel army classified in the United States as a terrorist group.

Al-Kassar, 61, and his cohorts believed "the arms deal was absolutely real," U.S. Attorney Michael Garcia said at a news conference in New York. "They demonstrated their willingness to support a terrorist organization and their capacity to do so."

The defendant, a longtime resident of Spain, was arrested Thursday evening at Madrid's Barajas airport after he arrived on a flight from the southern resort city of Malaga, officials said. On Friday, investigators searched his palatial home in Marbella, near Malaga.

"Someone who considered himself untouchable is now sitting in a jail in Spain," said Karen Tandy, the DEA administrator.

Two other men indicted in Manhattan's U.S. District Court, Tareq Mousa al Ghazi and Luis Filipe Moreno Godoy, were arrested in Romania, officials said.

During the sting, more than $400,000 was wired from New York to Spain as down payment, but no weapons ever changed hands, officials said.

Al-Kassar went before a Spanish judge in Madrid on Friday. There were no immediate details on extradition proceedings, though Spain and the United States do have an extradition treaty that applies in such cases.

The indictment from a New York federal grand jury charges al-Kassar with conspiracy to provide aid and equipment to a terrorist organization, conspiracy to kill U.S. citizens and officials, conspiracy to acquire and use anti-aircraft missiles and money laundering. The men arrested in Romania face the same charges; no other details about them, including their nationalities, were immediately available.

The indictment said al-Kassar has provided weapons and military equipment to violent factions in Nicaragua, Brazil, Cyprus, Bosnia, Croatia, Somalia, Iran and Iraq.

"Some of these factions have included known terrorist organizations, such as the Palestinian Liberation Front," the indictment said, "the goals of which included attacks on United States interests and United States nationals."

Al-Kassar's weapons-trafficking business included "an international network of criminal associates, front companies and bank accounts," the indictment said.

In addition to "bombings, massacres, kidnappings and other acts of violence within Colombia," the revolutionary group, known as FARC, is "the world's largest supplier of cocaine," the indictment said.

Al-Kassar is also reportedly on the Iraqi government's most-wanted list for allegedly arming insurgents, and has been accused of aiding militants in many of the world's bloodiest conflicts.

In an interview in October of last year with the British newspaper The Guardian, al-Kassar acknowledged he was friends with an alleged leader in the Iraq insurgency who was a relative of Saddam Hussein, but insisted he knew nothing of the man's role in fighting against the U.S. occupation.

Al-Kassar, who gave the interview at his home in Marbella, said that if the charges were true and he did back the insurgency, it would be "an honor," but he denied the allegations.

"If it were true," al-Kassar told the newspaper, "you would not find me here."

Al-Kassar stood trial in Spain in 1995 on charges he supplied assault rifles used by Palestinian militants in the hijacking of the Italian cruise ship Achille Lauro in 1985, but was acquitted for lack of evidence.