TUNIS, Tunisia (AP) — Four suspects belonging to a radical Islamic group have been arrested for their alleged involvement in the murder of a leftist politician that plunged Tunisia into crisis, but the killer himself remains at large, the interior minister said Tuesday.

Ali Larayedh, who has been tapped to be the next prime minister, said the Tunisian suspects, some of whom had been arrested in the last 48 hours, were accomplices to the murder and that the identity of the assassin is known.

The assassination of Chokri Belaid, an opposition politician from the Popular Front coalition, occurred outside his home on Feb. 6. It shocked the country, and many blamed the Islamist-led governing coalition, unleashing days of protests. On Sunday, thousands demonstrated in downtown Tunis over the lack of results in the investigation.

Many have accused the moderate Islamist Ennahda Party, which dominates the government, of complicity in the attack, citing its alleged use of gangs to intimidate political opponents. But Ennahda has denied ever resorting to any violence and has vehemently condemned the assassination.

Larayedh, who is a member of Ennahda, did not identify the group he was holding responsible for the assassination, but denied there were any foreign links to the killing.

Since the overthrow of Tunisia's secular dictatorship in January 2011, there has been a rise in ultraconservative Muslims known as Salafis, some of whom have resorted to violence. On Sept. 14, a band attacked the U.S. Embassy and damaged the surroundings. Tunisia's government has blamed the radical Islamic group Ansar al-Shariah for that attack and said it is trying to track down its leader.

Larayedh said that he was holding Tuesday's news conference in response to pressure for results of the investigation and media leaks the night before that had erroneously claimed the murderer himself had been arrested.

"The investigation is ongoing, and I will give you the latest conclusions," he said. "We cannot give any details that would affect the inquiry."

The four suspects range in age from 26 to 34 and are part of a "radical religious group," the minister said, adding that one had confessed to accompanying the actual assassin. At least some of the others detained had been involved in checking out the site a few days before the attack, the minister said.

Belaid was shot four times as he got in his car outside his house. The suspect involved in the actual attack took part in a reenactment of the crime scene outside Belaid's home on Tuesday wearing a mask and under heavy police guard.

"It was an ignoble crime with repercussions on the country's security and social peace, and has threatened to take us into chaos and the unknown," Larayedh said at the press conference.

The assassination resulted in the resignation of the country's prime minister, and Larayedh has been appointed his successor to form a new coalition government.

Authorities also have discovered many weapons caches and clashed with militants crossing into the country from neighboring Algeria and Libya. Larayedh said he believes some of the weapons were to carry out terrorist attacks inside Tunisia, while others were en route from Libya to Islamist militants fighting in northern Mali.