WASHINGTON 

The US on Thursday condemned reports that Russian forces had taken staff of the Chernobyl nuclear waste storage facility in Ukraine hostage and called for their release.

"We’re outraged by credible reports that Russian soldiers are currently holding the staff of the Chernobyl facilities hostage," White House spokeswoman Jen Psaki said at a press briefing.

"This unlawful and dangerous hostage taking, which could end the routine civil service efforts required to maintain and protect the nuclear waste facilities, is obviously incredibly alarming and greatly concerning. We condemn it, and we request their release," she added.

Earlier, Ukraine’s presidential adviser Mykhailo Podolyak said Kyiv had lost control of the power plant in the country’s north after a fierce battle with Russian forces.

Speaking to Ukraine's Unian news agency, Podolyak said the latest Russian move constitutes one of the biggest threats to European security.

The military intervention by Russia in Ukraine was announced early Thursday by President Vladimir Putin, and on the first day of the operation, more than 130 people including civilians were killed, according to Ukrainian President Volodymyr Zelenskyy.