Aid groups said this week Sudanese security forces blocked flights and road trips in Darfur, stranding staff and stopping food deliveries.
Sudan's mostly desert Darfur region is seven years into a conflict that started in 2003 when mostly non-Arab rebels took up arms against Sudan's government, demanding more autonomy.
Aid groups set up the world's largest humanitarian operation to care for hundreds of thousands driven from their homes by the rebellion and a fierce counter insurgency waged by government troops and allied, mostly Arab, militias.
European Commissioner for International Cooperation, Humanitarian Aid and Crisis Response, Kristalina Georgieva, speaking to Reuters after a four-day visit to Sudan, said Sudanese authorities had turned down 26 of more than 30 recent requests for aid road trips in South Darfur state.
Flights were also being blocked, she said.
"We are calling on the government to allow the Red Cross and other humanitarian organizations that are key to get into more remote areas," she said by phone from Kampala. "One in five or one in six requests were granted... They have to shift more toward access being the rule rather than the exception."
She said some aid groups were equipped to work in dangerous areas and needed to reach civilians affected by violence.
No one was immediately available for comment from Sudan's humanitarian affairs ministry or the South Darfur government.
Violence spiked after Darfur's Justice and Equality Movement rebels suspended their participation in peace talks in May. UN figures showed almost 600 people died in rebel and tribal clashes that month, mostly in southern and central Darfur, making it the region's bloodiest month for more than two years.
"The fact is that insecurity is worsening and that the populations in the camps is increasing as a result of more people fleeing more dangerous areas... Darfur must not be forgotten," said Georgieva.
