LONDON - A spokeswoman for British Prime Minister Theresa May said here Thursday that an investigation is under way to determine what happened in the hoax call to Foreign Secretary Boris Johnson by pranksters claiming to be Armenian prime minister.

The spokeswoman made the remarks after Johnson has been duped into discussing Britain's relationship with Russia with hoax callers pretending to be the Armenian prime minister.

Johnson held an 18-minute phone call with the prankster.

An audio clip posted online by Russian pranksters, Lexus and Vovan, appears to show the foreign secretary talking about Russian President Vladimir Putin and the poisoning of the Skripals. The pranksters were pretending to be Nikol Pashinyan, the recently elected political leader in Armenia.

The British Foreign Office said Johnson had ended the call when he realised it was a hoax and issued a stern statement condemning the "childish actions" of the duo.