JUBA (Sudan) (AFP) - South Sudan's Defence Minister was killed on Friday in a plane crash along with at least 22 other people, most of them senior members of the southern former rebel leadership. The UN Secretary-General's Special Representative in Sudan, Ashraf Jehangir Qazi, expressed his condolences over the "tragic" plane crash, according to a UN statement. It said that UNMIS had made aircraft available to take southern safety officials to the scene of the crash. Lt-Gen Dominic Dim Deng's plane came down 375km from the southern capital Juba, killing everyone on board, including many army officers. "There were 21 passengers besides the pilots," southern president Salva Kiir told journalists in Juba. He said there were probably two crew on board but that "the full list of the passengers is not yet obtained. We have confirmed, however, that Lieutenant General Dominic Dim was among the passengers," along with his wife. Kiir's spokesman Luka Mariak told AFP earlier that the plane came down "in a flat, savannah-like region." Kiir said that the United Nations Mission in Sudan (UNMIS), which sent a helicopter to the scene of the crash, confirmed that all on board were killed. "With this tragedy, I declare public mourning all over southern Sudan for three days," Kiir said. South Sudan Vice-President Riek Machar told AFP that he did not know the reason for the crash, but ruled out an attack. Mariak said the crash appeared to be due to a mechanical failure. Justin Yak, Minister for Cabinet Affairs until he was dropped in a reshuffle in 2007 because of ill-health, also died in the crash along with his wife. Distraught relatives gathered at Juba airport waiting for news in the hours following the crash. Government offices in the town were closed amid a pervasive mood of gloom, an AFP correspondent reported. Late on Friday, Juba airport was deserted with the bodies of the dead now expected to be flown to the nearby UNMIS airfield which is off-limits to the public. "The plane had been rented from a charter company and was carrying a delegation of leaders from the (former rebel) Sudan People's Liberation Movement from Wau to the capital Juba," 450km to the southeast, Machar said. Machar said an inquiry would be opened into Friday's crash. There was no immediate reaction to the crash from the central government in Khartoum, against which the SPLM fought Africa's longest-running civil war, which ended with a peace accord in 2005. The SPLM said that most of the leaders on the plane were from Twic, in central Sudan that provided many of the foot soldiers in the 21-year north-south conflict. Deng signed up to the national army in Khartoum in 1972 and rose to the rank of colonel before joining the SPLM's armed wing, the SPLA, in 1987, according to the Sudan Tribune, which added he moved to London in 1992.