UNITED NATIONS -Since fighting broke out in Sudan in mid-April, more than 2.6 million people have fled their homes, with more than 560,000 of them becoming international refugees, UN humanitarians said on Thursday. According to the UN Office for the Coordination of Humanitarian Affairs (OCHA), more than 2.1 million people were internally displaced since April 15, including 1.4 million people who fled the capital Khartoum. More than 560,000 people fled across the border into neighboring countries, mainly to Egypt, Chad and South Sudan. OCHA said humanitarian organizations reached more than 2.8 million people nationwide with food, nutrition, health, water and protection services. However, humanitarian partners say they are impeded in their work by insecurity and limiting bureaucratic access, including the lack of visas for international non-governmental organization personnel. "Attacks against humanitarian premises and warehouses, continue to hamper our ability to safely deliver aid," OCHA said. "We face tremendous difficulties in reaching people in conflict-affected areas in Khartoum, Darfur and Kordofan." The office said that since the start of the crisis, 13 humanitarian workers have been killed and many more injured. Some humanitarian personnel are missing. Partners of the United Nations reported that the looting of 43 humanitarian warehouses has made it challenging to resume and scale-up aid operations. The office said it continues to facilitate the movement of relief supplies from Port Sudan and across conflict lines. Between the end of May and the end of June, 480 trucks carrying about 19,700 metric tons of aid were delivered to Al-Jazirah, Khartoum, Gedaref, Kassala, Sennar, Northern State, River Nile and Blue Nile states. The World Food Programme (WFP) said it delivered emergency food and nutrition assistance to more than 1.2 million people in 14 of Sudan's 18 states, including some hard-to-reach areas in Darfur. Despite access challenges, the WFP said it has supported more than 420,000 people in the Darfur region with emergency food assistance and nutrition support. West Darfur remains largely inaccessible, and the WFP hubs and stores have been largely looted and destroyed. The UN agency said it delivered food assistance to around 50,000 people trapped in the Khartoum metropolitan area, with plans to support 500,000 as the security situation allows. The UN Refugee Agency (UNHCR) reported that more than 200,000 people have fled into neighboring Chad, including both Sudanese and Chadians who previously fled into Sudan from their country. Before the fighting in Sudan, Chad hosted nearly 600,000 refugees, including 400,000 from Sudan. The refugee agency and the Chadian government relocated people from the border area exposed to flooding and security risks, UNHCR said. The UN relief chief, Martin Griffiths, allocated 6 million U.S. dollars from the UN Central Emergency Response Fund for Chad, to support host communities in eastern Chad in their lean season in need of food and livelihood support following floods and the impact of the Sudan crisis.