Tunisian security forces arrested a suspect in the murder of opposition politician Mohamed Brahmi, an interior ministry spokesman told the AP news agency.
The security forces "surrounded a house [near the capital Tunis] where a terrorist group had holed up. Following a sustained exchange of fire, four elements were arrested," Mohamed Ali Aroui, the spokesman, told the AFP news agency on Sunday.
"Among them is Hmed el-Melki, alias 'Somali,' one of the elements implicated in the assassination of the martyr Mohamed Brahmi," he said, adding that weapons were seized during the raid.
"The interior ministry stresses that it was a successful operation," the spokesman said without revealing the identities of the other suspects.
Brahimi was killed outside his home last July, months after the assassination of another opposition politician, Chokri Belaid in similar circumstances.
Last Tuesday the government said that the suspected assassin Belaid had been killed in a police raid.
Authorities blamed the murders on Ansar Al-Sharia, a group accused of links to al-Qaeda, but the group has never said it was involved.
Belaid was a charismatic left-wing politician and virulent critic of the Islamist party Ennahda.
The assassinations eventually forced Ennahda to relinquish power last month in the face of accusations from the mainly secular opposition that it had failed to tackle a surge of violence since the Arab Spring revolution of 2011.
Ennahda won Tunisia's first free elections in October 2011, following an uprising to remove Zine El-Abidine Ben Ali from the presidency.
Brahmi's widow, speaking on Saturday during a rally marking the first anniversary of Belaid's funeral, accused the authorities of having "done everything to wipe out the traces of the crime".