"A Malaysian aircraft traveling from Western Europe to Kuala Lumpur … was apparently shot down," Biden said, telling the crowd he wanted to emphasize the information was based off of initial reports.
"Not an accident. Blown out of the sky," he said.
Biden addressed the airline disaster at the top of his keynote address before progressive activists at the 2014 Netroots Nation conference. He was nearly an hour late to the event after speaking to Ukrainian President Petro Oleksiyovych Poroshenko over the phone, to whom he offered U.S. assistance in probing the cause of the crash.
Biden said the top priority for the U.S. government was confirming reports that 23 American citizens were on board the plane.
"We've seen reports that there may have been American citizens on board and obviously that's our first concern," Biden said. "They're now working every minute to try and confirm that as I speak."
"This is a grave situation. Nearly 300 souls have been lost," he said. "The families need consolation and our prayers."
Biden also urged caution as the cause of the plane's crash, and if anyone is responsible, is confirmed. "There are many questions that need to be answered," he said. "My heart goes out to those families."
See updates on the situation below: