(Adds Larayedh quote, details, background)
By Tarek Amara
TUNIS, Aug 27 (Reuters) - Tunisia has declared Ansar al-Sharia a terrorist organisation after obtaining proof it killed two secular politicians and several soldiers, Prime Minister Ali Larayedh said on Tuesday.
Ansar al-Sharia is the most radical Islamist group to emerge in Tunisia since secular autocrat Zine al-Abidine Ben Ali was toppled in 2011. Its attacks have posed a challenge to the authority of the moderate Islamist-led government.
"We have discovered proof that the Ansar group is responsible for the assassinations of Chokri Belaid and Mohamed Brahmi and the attacks at Mount Chaambi," Larayedh told reporters.
"We have decided to officially classify this group as a terrorist group. Anyone belonging to it must face judicial consequences," he said.
Ansar leader Saifallah Benahssine, also known as Abu Iyadh, is a former al Qaeda fighter in Afghanistan sought by police for allegedly inciting an attack on the U.S. embassy in Tunis in September 2012.
Four people were killed in those disturbances, which began as a protest over a film that mocked the Prophet Mohammad.
Ansar al-Sharia has been suspected in the two assassinations and violent attacks in the Mount Chaambi area near the Algerian border, including the killing of eight soldiers last month.
Those killings and the assassinations of leftist secular leaders Belaid in February and Brahmi in July plunged Tunisia into political turmoil which political leaders are struggling to resolve. Police said the two politicians were killed with the same gun.
The Tunisian military has carried out air strikes this month on Islamist militants holed up in the Mount Chaambi area, scene of a hunt for jihadi fighters since December.
Secular opposition critics have accused Tunisia's Islamist-led government, which until now had refrained from calling Ansar al-Sharia a terrorist group, of laxity in fighting jihadi militants sowing insecurity in the country. (Reporting by Tarek Amara, writing By Tom Heneghan; Editing by Alistair Lyon)