"The United States, along with our international partners, is calling on the government of Kosovo to extend the deadline for implementing the new license plate regime," the State Department website said in a statement.
According to the US diplomat, Kosovo and Serbia should work urgently and with maximum flexibility to "reach a comprehensive agreement on the normalization of relations based on mutual recognition."
Earlier, the Prime Minister of the unrecognized Kosovo, Albin Kurti, announced Pristina's intention to join NATO and the European Union.
Since August 1, Serbian documents have ceased to be valid in Kosovo.
According to Russian Foreign Ministry spokeswoman Maria Zakharova, Kosovo's decision to apply rules on the forced replacement of Serbs' personal documents from August 1 is a step towards their expulsion from the region.
Serbian President Aleksandar Vucic said that Belgrade is ready to partially accept Pristina's requirements for entry documents.