NAIROBI- South Sudan has grounded planes belonging to United Nations peacekeepers in a dispute over control of the airport in the capital Juba, a government spokesman said on Monday.The move threatens to further delay the deployment of the latest 4,000 peacekeepers to be assigned to the African country, where civil war broke out in 2013."It was because the forces that were brought went to the airport to control the airport, which is not part of their mandate," President Salva Kiir's spokesman Ateny Wek Ateny said, explaining the decision to stop UN flights."They cannot come here to control our airport. It is our airport and if they wanted to cooperate with us, they must refrain from (deploying in) places they are not authorized."Government forces are currently in control of the airport. UN officials were not immediately available to comment.The UN Security Council agreed in August last year to deploy the so-called regional protection force of 4,000 extra peacekeepers, mostly from Rwanda and Ethiopia, after renewed heavy fighting broke out between troops loyal to Kiir and those backing former Vice President Riek Machar.The RPF was to supplement a 12,000-strong UN force already on the ground, but South Sudan has been reluctant to accept it, saying it has reservations over the nationalities of the troops and the armaments they can carry.A small batch started trickling in three months ago, but diplomats said the latest dispute could bring further delays.The UN peacekeeping mission known as UNMISS has been in South Sudan since its independence from Sudan in 2011. The country spiraled into civil war, with fighting along ethnic lines, after Kiir sacked Machar in late 2013.A peace accord was signed in August 2015 and Machar returned to the capital in April last year to share power with Kiir, before the deal fell apart less than three months later and Machar and his supporters fled the capital.The conflict has forced about 4 million people to flee their homes. Uganda currently hosts more than a million South Sudanese refugees, while over 330,000 have fled to neighboring Ethiopia.