BELGRADE (AFP) -- Serbian police arrested on Saturday one of the key suspects in the 2003 assassination of reformist prime minister Zoran Djindjic, the Interior Ministry said.

"After an intensive search, Aleksandar Simovic was arrested in a police operation in Belgrade early Saturday," the ministry said in a statement.

One of 13 people suspected of involvement in Djindjic's murder on March 12, 2003, Simovic has since been at large. The statement said he would be handed over to justice officials.

Simovic, 30, who has so far been tried in absentia before the Special court dealing with organized crime, was arrested in a flat in the capital's residential area New Belgrade, along with another man, police said.

Serbian state television showed footage of handcuffed Simovic being taken out from the building by special policemen and driven away in a patrol wagon.

The main defendants in the trial for Djindjic's murder are the alleged mastermind, elite police commander Milorad "Legija" Ulemek, and the alleged gunman, former special police officer Zvezdan Jovanovic.

Both Ulemek and Jovanovic pleaded not guilty at the trial that opened in December 2003, but has been delayed several times due to changes in the prosecution, a judge and obstruction by defense teams.

Five other suspects remain at large, among them Simovic's brother, Milos.

The Simovic brothers are suspected of being involved in the June assassination of a protected witness who had become witness for the prosecution and a number of still unsolved murders and other crimes, including kidnapping a businessman in 2001, police said.

For three and a half years, Simovic and his brother were believed to be in hiding in the bordering area between Serbia and Bosnia, as well as Bulgaria, Albania and Montenegro, local media reported.

A spokeswoman for the Special court said Simovic was expected to appear before judges next week and enter his plea. Simovic's arrest has come after a two-day hearing of Dejan "Bugsy" Milenkovic, a key defendant in the trial, who confirmed the indictment that Ulemek, an alleged mafia kingpin, was behind the plan to kill Djindjic.

Milenkovic also claimed that two senior Serbian politicians had known of a plot to murder Djindjic, insisting that the "reason for the assassination was their (Ulemek's and others) fear of arrest... with the goal of overthrowing the government, creating chaos and bringing" ultra-nationalist forces to power.

His testimony, which began on Thursday, came after he had reached a deal with the prosecution to become a special witness under still unpublished deal. He is also the only suspect to have pleaded guilty to the charges.

Milenkovic also said the gang, known in the underworld community as Zemun gang, had been planning bomb attacks on the main Belgrade power plant, several important traffic intersections and the U.S. embassy in the Serbian capital.

Milenkovic had been tried in absentia at the beginning of the trial but after his arrest in Salonika, he was last year handed over to Serbia by Greek authorities.

Djindjic led Serbia's first democratic government after the ouster of former autocratic president Slobodan Milosevic in October 2000, but it collapsed less than a year after his murder.