Police hunting for the assassins of Serbia's prime minister rounded up more than 70 suspected mob figures Thursday and detained two of Slobodan Milosevic's former senior security chiefs.

The arrests came a day after Zoran Djindjic, 50, was gunned down in Belgrade. The prime minister had made enemies for his pro-Western stance and for declaring war on the organized crime that flourished both under and after former Serb leader Milosevic, now in the Netherlands on trial for Balkan war crimes.

In their first statement since the assassination, police said the arrested suspects had links to an underworld group targeted by Djindjic's anti-corruption campaign.

The government has accused Zemun Clan -- a shadowy crime group including former paramilitaries loyal to Milosevic -- of masterminding the attack on Djindjic and several other unsolved murders.

"I assure you we will arrest all responsible and liquidate anyone who resists arrest," said Dusan Mihajlovic, Serbia's interior minister.

Acting Prime Minister Nebojsa Covic said more than 70 people were detained, among them former state security chief Jovica Stanisic and his deputy, Franko Simatovic, who was led from his Belgrade home by three hooded policemen with machine guns.

Before being ousted in late 1990s, Stanisic, then head of Serbia's secret service, and Simatovic, who formed a dreaded paramilitary unit known as the Unit For Special Operations, led Milosevic's paramilitary campaigns in Croatia and Bosnia.

The two were believed to have maintained significant influence in the police and in mob circles even after the former Yugoslav president's ouster in 2000.

Still at large, despite a manhunt, were the main Zemun Clan suspects, including group leader Milorad Lukovic, who succeeded Simatovic as commander of the Unit for Special Operations. The group committed atrocities against civilians during the 1990s wars in Croatia, Bosnia and Kosovo.

Lukovic and his associates also are suspected of being behind attacks on Milosevic's opponents during the former dictator's rule -- the attempted murder of opposition leader Vuk Draskovic in 1999 and the 2000 abduction of former Serbian President Ivan Stambolic, not been seen or heard from since.

Arrest warrants for Lukovic and other underworld bosses were to have been signed on the day of Djindjic's assassination.

Across Belgrade, citizens and politicians mourned the prime minister, who played a key role in ousting Milosevic in October 2000 and extraditing him to the U.N. war crimes tribunal the following year.

Hundreds of Belgraders lined up in front of the government building, laying flowers and lighting candles at the spot where Djindjic was killed as he stepped from his armored car. Not far away, Djindjic's Democratic Party held a memorial service, pledging to continue his reformist policies.

An initial investigation showed there were three attackers who wore dark blue overalls with yellow labels. One was armed with a sniper rifle, the other two with handguns, police chief Milan Obradovic said.

The three fired at Djindjic through the open window of a room on the second floor of a nearby building and then fled on foot, he said. The snipers were not identified.

Serbian authorities gave police and army a free hand in the investigation, introducing a state of emergency that allows suspects to be arrested without a warrant and detained for up to 30 days without charges.

Armed with assault rifles, police at checkpoints throughout the capital searched cars and drivers. The army also pledged to help in the investigation, amid fears the country could plunge into violence in a possible power struggle for Djindjic's successor.

The government said Thursday the chairmanship of the Cabinet would be rotated until parliament elects a new prime minister. Covic, one of five deputy prime ministers, took the helm only initially.

The party of former Yugoslav President Vojislav Kostunica, Djindjic's political foe, criticized the state of emergency, calling it an "extreme and potentially hazardous measure." It called for the formation of a transitional government.

There also were concerns that Djindjic's death could jeopardize Serbia's cooperation with the West and block badly needed foreign investment. But finance minister Bozidar Djelic said the reforms would continue.