Russian officials says twin suicide bombings have struck outside Kabul's airport, killing at least 13 people.
Large crowds of people trying to flee Afghanistan have massed at the airport.
Western nations had warned earlier in the day of a possible attack at the airport in the waning days of a massive airlift.
Suspicion for any attack targeting the crowds would likely fall on the Islamic State group and not the Taliban, who have been deployed at the airport's gates.
Russia's Foreign Ministry gave the first official casualty count, saying 13 people had died and 15 were wounded.
U.S. officials said that American personnel were wounded in the blast, without elaborating.
They spoke on condition of anonymity to discuss ongoing operations.