Hundreds of elite US mercenaries are reportedly taking part in Ukraine's military operation against pro-Russian activists in southeastern regions. German media say four-hundred American employees of the US private security firm, Academi, formerly known as Blackwater, are involved in the crackdown. The Americans have been reportedly deployed near the town of Slav-yansk in the Donetsk region. Kiev has launched the operation to force pro-Russian activists out of state buildings they have been occupying in the region.