US Secretary of State Antony Blinken has suggested Russian security services were behind an attack on a Nobel Peace Prize-winning Russian journalist last month.

Dmitry Muratov, the editor-in-chief of the Russian newspaper Novaya Gazeta, was splashed with what appeared to be paint on April 7. Muratov has taken a critical stance toward the Russian government.

Speaking to reporters on World Press Freedom Day on Tuesday, Blinken said US intelligence assessed that the attack was "the work of Russian intelligence."

He said "it sent a clear message to others considering criticizing the Kremlin's war of aggression against Ukraine."

Blinken pointed out that Moscow is trying to hide the truth about its onslaught on Ukraine.

He said it is important that journalists inform the world about what is actually happening so it can understand the "brutality" and "inhumanity" of Russia's aggression.

He added that such reporting "has a way of putting pressure on those who are engaging in these actions to change course."