LONDON (AP) — Britain's Foreign Office on Thursday criticized "childish" Russian pranksters who phoned Foreign Secretary Boris Johnson posing as the leader of Armenia.

The Guardian newspaper said that Johnson was called by Alexei Stolyarov and Vladimir Kuznetsov, known as Lexus and Vovan.

One pretended to be new Armenian Prime Minister Nikol Pashinian, and the newspaper said that Johnson spoke to them for 18 minutes, discussing topics including the poisoning of ex-spy Sergei Skripal.

The pair released audio of the call, which they said took place last week. In it, Johnson laments the poor state of U.K. relations with Russia, saying Moscow seems "unable to resist malign activity one kind or another."

The Foreign Office said Johnson "realized it was a hoax, and ended the call. We checked it out and knew immediately it was a prank call."

"The use of chemical weapons in Salisbury and Syria and recent events in Armenia are serious matters," it said in a statement. "These childish actions show the lack of seriousness of the caller and those behind him."

Stolyarov and Kuznetsov, who have fooled high-profile victims around the world, have denied links to Russia's security services. In 2015, they phoned Elton John pretending to be Russian President Vladimir Putin after the musician criticized Russia's stance on gay rights.