Tunisian police have identified the killer of opposition leader Chokri Belaid as a member of a radical Islamist Salafi group who is on the run, Prime Minister-designate Ali Larayedh said on Tuesday.
Larayedh, who remains Interior Minister until his government is formed, told a news conference police had arrested three accomplices who are also ultra-orthodox Salafis.
The assassination of secular politician Belaid on Feb. 6 ignited the biggest street protests in Tunisia since the overthrow of strongman Zine al-Abidine Ben Ali two years ago.
A security source said on Monday a Salafi had been arrested in connection with the killing, while Tunisia's Express FM radio cited a senior security official as saying police had arrested three Salafis, including a police officer, over the murder.
"Now we have identified the killer of Belaid and he is on the run. The police are looking for him," Larayedh said.
One of the arrested suspects had accompanied the gunman who shot Belaid outside his home before escaping on a motorcycle, he said, adding that the group had mounted surveillance of Belaid's home and a nearby square for several days before the attack.
The Interior Minister did not confirm the Express FM report that one of those detained was a police officer.
"Identifying the killers of Belaid reinforces confidence in the judiciary and in the neutrality of security (forces)," said Larayedh, who belongs to the moderate Islamist Ennahda party.
After his announcement, Belaid's widow Basma said it was still not clear who had orchestrated her husband's assassination, which was the first in Tunisia for decades.
"It's good to know who killed Chokri, but it is very important to know who gave the order because it was a very organised crime," she told Europe 1 radio in Paris.
No one has claimed responsibility for the killing. Ennahda and the Interior Ministry have denied accusations by some in the opposition that they were behind it.
Last year, Salafi groups prevented several concerts and plays from taking place in Tunisian cities, saying they violated Islamic principles. Salafis also ransacked the U.S. Embassy in September, during international protests over an Internet video.
Secular groups have accused the Islamist-led government of a lax response to Salafi attacks on cultural venues and individuals in recent months.
After Belaid's death, Prime Minister Hamadi Jebali tried to restore calm by proposing an apolitical cabinet of technocrats to organise a parliamentary election, but resigned after opposition from within his own Ennahda party scuppered the plan.
On Friday, President Moncef Marzouki asked Ennahda's nominee Larayedh to form a new government within 15 days.
The so-called Jasmine Revolution that toppled Ben Ali in January 2011 was the first of several Arab uprisings.
Tunisia's political transition has been more peaceful than those in other Arab nations such as Egypt, Libya and Syria, but tensions are running high between Islamists elected to power and liberals who fear the loss of hard-won liberties.
While Islamists did not play a major role in the Tunisian revolt, the struggle over Islam's role in government and society has emerged as one of the most divisive political issues.
Salafis, some of whom sympathise with al Qaeda, want a broader role for religion in Tunisia, alarming secular elites who fear they will seek to impose their strict views at the expense of individual freedoms, women's rights and democracy.