Tunisian authorities have identified and are pursuing the main suspect in the assassination of leading Tunisian left-wing politician Chokri Belaid, Interior Minister Ali Laarayedh has confirmed.   Four men, believed to be accessories to Belaid's murder have been arrested, and all four belong to extremist Salafist groups, the minister told reporters. Laarayedh also revealed that individuals involved in Belaid's surveillance before his fatal shooting have been identified and apprehended. The suspects' ages range from 26 to 34, and one of them was a member of a gang which attacked people and property in violence following the Tunisian revolution.