Juba - Two Kenyan pilots have been seized by rebels in South Sudan after their plane crash-landed, killing one person, the UN said on Wednesday."There are negotiations on-going, mainly between the company that owns the aircraft and the SPLA-IO (a rebel group)," said David Shearer, head of the UN Mission in South Sudan (UNMISS), at a press conference in the capital Juba."As negotiations are going on I don't want to make any comment, it may jeopardise the arrangements," he added. The SPLA-IO has been fighting a devastating four-year war against the government. The violence has caused tens of thousands of deaths and forced more than a million people to flee the country.Details about the crash landing are sketchy but the website of Kenyan paper The Standard says the plane suffered technical problems and came down a few minutes after takeoff.Nine employees of a South Sudanese NGO were on board, the paper said, who were returning to the capital Juba after a mission in the rebel-held region of Akobo, close to the Ethiopia border. The passengers and pilots received minor injuries, it reported.The plane crashed two weeks ago, killing an old man and also hitting two cattle pens, according to SPLA-IO deputy spokesperson Lam Paul Gabriel.The pilots were detained because the family of the deceased and owners of the cattle are demanding "compensation", he added.The Standard reports the plane killed a woman - not a man - and also hit 11 cows, and says a payment of $198169.60 is being demanded in exchange for the pilots' release."The local chiefs have been directed to solve the problem. We don't want to use this opportunity to extort money from the company of these pilots," the rebels' spokesperson said."There are already talks on the way, the company is now involving our representative in Nairobi."South Sudan's leaders fought for decades for independence but once they achieved it, in 2011, a power struggle between former vice president Riek Machar and President Salva Kiir in 2013 led to an all-out civil war.A peace deal collapsed in July 2016 after fresh fighting in Juba forced then first vice president Machar into exile.