MOSCOW, May 16 (Xinhua) -- Moscow on Wednesday urged Washington to demand the release of Russian journalists detained in Ukraine.

Russian Foreign Ministry Spokeswoman Maria Zakharova was quoted by TASS news agency as saying that the U.S. state department should insist on the release of the journalists instead of being lenient to the Ukrainian government.

U.S. Department of State Spokesperson Heather Nauert earlier told reporters that Washington took the raid on journalists in Kiev "very seriously" and called for measures in full compliance with the law.

On Tuesday, the Security Service of Ukraine (SBU) conducted an operation against the RIA Novosti Ukraine news agency's staff, accusing them of state treason.

Also on Tuesday, Kirill Vyshinsky, a Russian citizen and editor-in-chief of the RIA Novosti Ukraine news agency, was detained near his home in Kiev. The agency's headquarters, its press center and homes of some of employees were also searched.?