The suspected murderer of Tunisian opposition leader Chokri Belaid has been identified and is on run but four of his accomplices have been arrested, Interior Minister Ali Larayedh said on Tuesday.
"The killer has been identified and is being chased," Larayedh told a news conference.
"Four other suspects have been arrested. They belong to a radical religious" group, said Larayedh, who is also prime-minister designate tasked with forming a new government.
Belaid's daylight killing on February 6 sparked deadly street protests and strikes and exposed the widening fissures between the ruling Islamists and liberals.
It also threw Tunisia into its worst political crisis since the revolution two years ago that ousted former strongman Zine El Abidine Ben Ali.
Larayedh said the four people arrested had "monitored (Belaid) for some time".
One of the suspects, he added, "confessed to having accompanied the killer on the day of the crime".
Police sources had earlier told AFP that those behind the killing were adherents of the Salafist movement, which is known for its radical version of Sunni Islam.
The Salafists have been blamed for several violent actions in Tunisia over the past months, including an attack on the US embassy last September that left four attackers dead.
Larayedh declined to comment on who may have ordered the killing, even as Belaid's widow urged authorities to get to flush out those responsible.
"It is good to know who carried it out, but for me it is very important to know who ordered it... because this was a very well-organised crime," Khalfaoui told France's Europe 1 radio during a visit to Paris on Tuesday.
"We are asking for a trial, for further investigation, for everything to be known," she said.
Belaid's brother, Abdelmajid, accuses the ruling Islamist Ennahda party of being behind the murder.
"It's Ennahda which gave the green light to kill my brother," he told AFP, but Khalfaoui was more cautious, saying only that "Ennahda's political leadership is involved".
The political crisis in Tunisia has been aggravated with Belaid's killing, with former prime minister Hamadi Jebali resigning after his own party Ennahda dismissed his proposal to form a new government of technocrats.