Mr. Laareyd did not disclose any details of the investigation but said that currently there is no certainty that those arrested committed the crime.
Belaid was shot outside his home in the capital of Tunis on February 6 which further aggravated the situation in the country where a confrontation between Islamists and secular forces has been raging for several months.
The opposition accused the Islamic movement of "An-Nadha" of eliminating political opponents.
Tunisian opposition leader Chokri Belaid killed on Wednesday was buried at the cemetery of el-Jellaz Friday.
Thousands of Tunisians attended the funeral and minor clashes with police erupted while the coffin was carried through Tunis.
Tunisia is now gripped with strikes and protests as people want the attackers to be punished and some demand the government’s downfall.
0Opposition leader's funeral brings day of reckoning for Tunisia
Tunisia's political crisis looked likely to deepen on Friday with strikes and protests planned around the funeral of assassinated opposition politician Chokri Belaid.
Belaid's killing on Wednesday has brought thousands of people onto the streets of the capital Tunis and other cities in violence-marred protests.
Unions have called a general strike for Friday, setting the stage for further confrontation two years on from the pro-democracy revolution that inspired the Arab Spring.
Tunisia is riven by tensions between the dominant Islamists and their secular opponents, and by disillusionment over the lack of social progress since the overthrow of dictator Zine al-Abidine Ben Ali in January 2011.
In response to Belaid's assassination, Prime Minister Hamdi Jebali, an Islamist, said on Wednesday he would dissolve the government, name a non-partisan cabinet of technocrats and hold early elections. But his partners opposed the move and it is yet to be approved by parliament.
Hundreds of protesters attacked and ransacked a police station in the Tunisian capital on Thursday in a second day of unrest over the killing of an opposition figure, witnesses said.
Hundreds of youths stormed the police station and threw its furniture, eeqipment and files into the street before fleeing, the witnesses said.
Voice of Russia, Reuters, AFP, TASS, RIA