Updated

Four suspects belonging to a radical Islamist group have been arrested for their alleged involvement in the murder of a leftist politician that plunged the country into a crisis, but the killer himself remains at large, Tunisia's interior minister said Tuesday.

Ali Larayedh 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.

Larayedh did not identify the radical Islamic 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.

Larayedh said all the suspects as well as the assassin were Tunisian. He also denied any foreign involvement, as had been alleged by some of Belaid's associates. "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," he said.

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.