South Sudan has withdrawn hundreds of police from the territory of Abyei that it disputes with Sudan ahead of a UN Security Council ultimatum, a UN spokesman said Friday. But the United Nations is still \"verifying\" the South\'s claim that it has withdrawn all forces from the small territory on the uncharted border between the two rivals, said the spokesman, Martin Nesirky. Abyei is one of a many disputes between South Sudan and Sudan that has brought the two sides close to all-out war. Khartoum troops seized most of Abyei a year ago. The United States welcomed South Sudan\'s withdrawal and said Sudan should now pull its troops out of the territory. The UN Security Council has given both sides until May 16 to withdraw their forces from Abyei and return to peace talks on all their disputes or face possible sanctions. The two Sudans have already missed one Security Council deadline to halt hostilities. Nesirky said the UN Interim Security Force for Abyei (UNISFA) had reported that South Sudan officially ordered the withdrawal of the South Sudan Police Service from Abyei on Thursday. About 700 South Sudan police have since relocated to South Sudan with the UN mission\'s logistical support. \"The UN mission is in the process of verifying that all South Sudan police elements have withdrawn from the Abyei area,\" the spokesman added. UN officials said it could take days to confirm whether all the South\'s forces have left. Sudan and South Sudan both claim the border region with fertile grazing and some oil reserves. Sudan still has several hundred troops in Abyei and South Sudan has a similar contingent close to its border with the territory. South Sudan seceded from the north in July last year. The two sides have since been in an increasingly bitter showdown over Abyei, the border, sharing oil wealth and who pays debts built up while they were one country. The north and south fought a two-decade civil war up to 2005 in which more than two million people died. Susan Rice, the US ambassador to the United Nations, said the withdrawal of South Sudan\'s police was \"an important step toward ending the border dispute with Sudan.\" \"We call upon the government of Sudan to honor its acceptance\" of UN Security Council resolution 2046 on the inter-Sudan conflict \"including by redeploying all of its armed forces from Abyei and by immediately ending aerial bombardments in South Sudan.\" Rice said the bombardments were a \"clear violation\" of the resolution passed on May 2, which called for an immediate halt to hostilities. \"We urge all parties to abide by their agreement to a cessation of hostilities and the resumption of negotiations on outstanding security and political issues,\" the US ambassador said in a statement.