The Serbian government today sent bulldozers and police armed with Kalashnikov rifles to demolish a four-story shopping complex belonging to one of the alleged assassins of Prime Minister Zoran Djindjic.

The destruction of the shopping complex in the Belgrade suburb of Zemun -- headquarters of the mafia group accused of Djindjic's murder -- appeared designed to signal that the government will no longer tolerate the alliance of criminals and paramilitary groups that flourished in the 1990s during the rule of Yugoslav President Slobodan Milosevic. The high-profile crackdown took place as police also arrested dozens of alleged members of the Zemun clan, and interrogated several Milosevic-era security chiefs on their connections with organized crime.

"This is a clear message that there is no going back," said Dragan Bujosevic, a leading Serbian journalist who was close to Djindjic. "Serbian leaders now understand that if they lose this war, they themselves will be the next targets. They prefer to be alive rather than dead."

Bystanders cheered as bulldozers crashed into the glass-and-concrete shopping center illegally constructed by Dusan Spasojevic, reputed to be the right-hand man to Milorad Lukovic, the former head of an elite paramilitary group known as the Red Berets.

The government described both men as "fugitives from justice" after they disappeared along with dozens of their supporters following Wednesday's assassination of Djindjic.

Nicknamed Legija -- "Legionnaire" -- because of his earlier service in the French Foreign Legion, Lukovic amassed power and wealth during the 1990s as a leader of the paramilitary groups fighting a series of dirty wars in Croatia, Bosnia and Kosovo. The government has accused him and the Zemun clan of being behind a string of unsolved murders and kidnappings over the past five years.

After Milosevic's overthrow in October 2000, a new democratic government headed by Djindjic and then-ally Vojislav Kostunica promised to attack the roots of organized crime by reforming the police and judiciary. But little was done to break the power of the mafia, say Serbian analysts and Western diplomats, and many Milosevic appointees remained at their posts in the security services.

Djindjic, who was killed by snipers as he got out of his car in front of government headquarters, will be buried Saturday in a ceremony attended by many foreign delegations. The United States announced it is sending former secretary of state Lawrence S. Eagleburger, who served as ambassador here in the 1980s, to represent President Bush.

Serbian officials said that Djindjic is likely to be succeeded as Serbian prime minister by a close ally, Zivan Zivkovic, a former mayor of the southern town of Nis and a leader of the street uprising against Milosevic. Zivkovic earlier had been slated to take over as defense minister, a key post in any showdown with paramilitary groups.

Serbian officials said that Djindjic was planning a large-scale crackdown on the mafia and paramilitary groups in recent weeks, and suggested this could have been the motive of whomever was behind the assassination. Zivkovic's appointment as defense minister was seen as one of the final elements in those preparations to ensure army support in any attempt to disarm several hundred well-armed and highly trained paramilitary groups.

Although the government is now displaying newfound energy in its war on organized crime, some Serbian analysts and Western diplomats here are skeptical that it will last long. They note that the Interior Ministry remains under the control of Dusan Mihajlovic, a Communist-era apparatchik who has failed so far to solve any of the high-profile crimes of the past few years, and has shown little interest in tracking down alleged war criminals.

But the problem extends far beyond Mihajlovic, a former Milosevic ally who switched his support to the opposition in the period leading up to the October 2000 revolution. Judges and policemen are extremely poorly paid, resulting in almost endemic corruption in the security services, and little enthusiasm for tackling organized crime.

"We are still waiting for the fight against organized crime that was declared two and a half years ago to really begin," said Budomir Budovic, a leading expert on the Serbian police. "You can't replace 10,000 police officers overnight."

Lukovic's career with the Red Berets is typical of the close links between Serbian paramilitary groups and organized crime that go back to the early 1990s, during the violent breakup of Yugoslavia. After serving with the French Foreign Legion in Africa, Lukovic returned to Serbia in 1992, and joined a paramilitary group known as the "Tigers," which has been accused of war crimes in Croatia and Bosnia. He went on to found the Red Berets, a special operations unit under the command of the interior minister.

In an open letter published earlier this year, Lukovic accused the Serbian government of preparing to hand him and other "Serb patriots" over to the U.N. war crimes tribunal in The Hague. He suggested that this violated the terms of an agreement he reached with Djindjic in October 2002 when the Red Berets rejected orders from Milosevic to crack down on the opposition.

Police in a suburb of Belgrade surround a complex belonging to a suspect in the killing of Serbian Prime Minister Zoran Djindjic.