The United States on Friday demanded Russia "immediately" withdraw a convoy of vehicles from Ukraine and warned of further international sanctions if Moscow did not respect Kiev's sovereignty. Russia says the trucks are a humanitarian convoy shipping aid to the beleaguered civilian population in war-torn eastern Ukraine, but Kiev had not authorized their entry and has dubbed the move an invasion. "We condemn this action by Russia, for which it will bear additional consequences," said Caitlin Hayden, spokeswoman for the White House National Security Council. "This is a flagrant violation of Ukraine's sovereignty and territorial integrity by Russia. Russia must remove its vehicles and its personnel from the territory of Ukraine immediately." Hayden said the convoy should have been overseen by the International Committee of the Red Cross and alleged that pro-Russian rebels had blocked legitimate aid shipments. "At the same time as Russian vehicles violate Ukraine's sovereignty, Russia maintains a sizable military force on the Ukrainian border capable of invading Ukraine on very short notice," Hayden said. "It has repeatedly fired into Ukrainian territory, and has sent an ever-increasing stream of military equipment and fighters into Ukraine." Pentagon spokesman Rear Admiral John Kirby also condemned the Russian actions and warned that Russia would face further isolation or international sanctions. "Russia must remove its vehicles and its personnel from the territory of Ukraine immediately. Failure to do so will result in additional costs and isolation," he said. He described the convoy as a violation of Ukraine's "sovereignty and territorial integrity by Russia" and questioned whether the convoy was really on a humanitarian mission. "Russia should not send vehicles, persons or cargo of any kind into Ukraine, whether under the guise of humanitarian convoys or any other pretext, without Kiev's express permission," he said. It was unclear what cargo was being ferried to eastern Ukraine, he added. "We don't have a perfect picture of what's in those trucks," Kirby said. Local officials in Ukraine said 20 trucks rolled into the pro-Moscow rebel bastion of Lugansk, despite objections from Kiev. The move came as the UN Security Council planned to hold emergency consultations on the convoy.