Nairobi - An advance party of peacekeepers with a bolstered mandate to use force have arrived in South Sudan, the United Nations said on Monday, the first blue helmets with a greater authority to protect civilians in the troubled East African nation.At least 13 peacekeepers from a regional protection force mandated by the Security Council have arrived in the capital of Juba, Shantal Persaud, a spokesperson for the UN mission in South Sudan told The Associated Press.The troops will reinforce existing engineering operations and help to prepare camp sites for the 4 000 peacekeepers expected to arrive later this year, Persaud said."They are not troops but rather 'enablers,'" Persaud said by email, adding that the rest of the troop contingent is expected to arrive in June or July.South Sudan's government had earlier blocked the force from entering the country, claiming they are not needed and would violate South Sudan's sovereignty.The 4 000 strong regional protection force adds to the more than 12 000 peacekeepers who are already in South Sudan and have struggled to protect civilians. The extra peacekeepers were mandated by the Security Council after fighting in Juba in July last year killed hundreds of people and escalated the civil war across the country.Separately on Monday, the top UN humanitarian official in South Sudan, Serge Tissot, demanded protection for civilians forced to flee a recent government offensive in Kodok. Roughly 25 000 people have fled Kodok after heavy fighting in the area, according to the humanitarian organization Doctors Without Borders.Some UN supplies for civilians displaced from Kodok have been looted by opposition forces and others in recent days, Tissot said in a statement. Late last week a UN spokesperson, Daniel Dickinson, said that peacekeepers had been blocked from accessing the fighting area near Kodok.South Sudan has become the world's fastest growing refugee crisis due to its civil war that began in December 2013. Roughly 1.8 million people have fled the country.