Parliament late Friday approved new laws that allow police to detain suspects for up to 60 days without charges or judicial control. Zivkovic said the measure was needed to help prosecute crime bosses, paramilitary leaders and opposition leaders allegedly involved in the March 12 slaying of Zoran Djindjic.
The measures sparked criticism among human rights groups, including the Council of Europe, which said the changes did not comply with European standards. The council recently accepted Serbia and Montenegro as a member.
But Zivkovic, in comments to the state-run Tanjug news agency, defended the measures.
"There is no danger that Serbia will become a police-run state … nor (that) there will be bans on political parties," he was quoted as saying. "But it may happen that somebody from the top of (opposition) parties is found guilty of taking part in activities of criminal groups" that allegedly killed Djindjic.
Serbia's state-run television reported late Friday that findings in the investigation "are leading toward a group of so-called patriotic forces including the Democratic Party of Serbia," headed by former Yugoslav president Vojislav Kostunica.
Kostunica and Djindjic jointly ousted former President Slobodan Milosevic in 2000 but later turned against each other. Kostunica has denied the allegations his party was involved in the killing and claimed he was a victim of a witch-hunt.
Authorities declared a state of emergency after the assassination and have rounded up more than 7,000 people, including two of Kostunica's associates — a security adviser and a former head of military intelligence.
The investigation initially focused on drug traffickers and Milosevic-era paramilitary fighters, who are accused of carrying out the assassination. Authorities say links between those groups and opposition figures indicate the killing was part of an attempt to overthrow the government.
Some of the extended police powers that came with the state of emergency were made permanent with the new laws approved Friday, sparking human rights groups and opposition leaders to warn against a return of Milosevic-style autocracy.
The New York-based Human Rights Watch said it was concerned by the new police powers and criticized the "long-term incommunicado detention … without access to a lawyer, family members, or judicial review of the detention order."
The group warned against such "police practices inherited from the Milosevic regime" and any "ill-treatment of detainees inflicted in order to extract a confession."
Milosevic's Socialist Party also warned in a statement that the harsh measures are "contrary to European standards and can easily lead to vast misuse."
Parliament could vote to remove the new laws in a review to be held in several months.
The Belgrade-based Humanitarian Law Center said scores have been rounded up "solely because of their past criminal records," without links to the murder.
Zivkovic, rebuffing those concerns, said the state of emergency would be revoked in a few weeks.
Polls show strong public support for the crackdown on Serbia's notorious underworld and tough new measures that envisage longer prison terms for an array of offenses and the confiscation of illegally acquired assets.
By Misha Savic