Russian President Vladimir Putin signed a decree on Monday recognizing the two eastern Ukrainian regions as independent states, drawing condemnation from the West and promises of sanctions.
Putin ordered troops into the regions for a peacekeeping operation, the details of which were not immediately clear. In the last few years, Russia-backed rebels have been fighting in Luhansk. Russia has denied having its own troops on the ground.
US officials have warned that Russia would try to get a pretext to launch an invasion. Putin claimed last week that genocide was happening in the province of Donbas, where Luhansk is located. Russia justified military intervention in Donbas by saying ethnic Russians were being threatened.
The White House said it would impose sanctions on anyone operating in the areas of Luhansk and the Donetsk in response to the actions of Putin.