MASERU (Reuters) - Lesotho s top military leader, Khoantle Mots omots o, and two  senior officers were shot dead on Tuesday at an army barracks, the government said. While it was not immediately clear what the motivation for the shooting was, the kingdom has been subject to several coups and periodic political violence since gaining independence from Britain in 1966, and South Africa called for calm. Colonel Tanki Mothae, the principal secretary for the defense force, told Reuters the two senior officers were under investigation for the murder of another former Lesotho defense commander in 2015. Prime Minister Thomas Thabane, who fled the country in 2014 after a coup attempt and whose wife was shot dead in June, offered no details about the killings during a news conference other than saying the incident was being investigated. Neither Mothae nor the prime minister confirmed South African media reports that the two officers had killed the defense commander and then died in a gunfight with soldiers. South African President Jacob Zuma condemned  in the strongest terms possible the senseless and regrettable killing  and called for  calm and restraint  in the mountainous country that is entirely surrounded by its large neighbor. Lesotho is a major supplier of water to South Africa s industrial heartland. Zuma also said the Southern African Development Community (SADC) would send a ministerial fact-finding mission to Lesotho on Thursday to assess the situation.      South African Deputy President Cyril Ramaphosa has made frequent trips to Lesotho to try to secure peace among political rivals as a facilitator for SADC.  Lesotho has been through bouts of political turbulence since the attempted coup in 2014 and its last three elections - most recently in June - have failed to produce winners with clear majorities.  