The British foreign secretary has been duped into speaking to two Russian pranksters on the phone for 18 minutes, discussing sensitive security matters such as the nerve agent attack in Salisbury.

The tricksters released audio of the call, in which one pretends to be the Prime Minister of Armenia, on Thursday – the day Russia was further implicated in the shooting down of the MH17 jet over Ukraine.

The pair, Alexei Stolyarov and Vladimir Kuznetsov, is thought to have links to the Russian government, although they deny this, The Guardian reports. They have previously targeted Turkish premier Recep Tayyip Erdoğan and spoken with Elton John, pretending to be Vladimir Putin.

Boris Johnson opens the call by congratulating the caller “very sincerely on your remarkable success”, thinking he is the newly elected Armenian leader Nikol Pashinyan.

Moving onto discussing Russia, he says, “obviously, we had hoped to have better relations… then we currently do,” adding: “I’m afraid that Russia seems to be unable to resist malign activity of one kind or another. ”

The foreign secretary even chuckles when the prankster said he is to meet the Russian president and “hoped he will not poison me with Novichok”, the deadly nerve agent used on Sergei and Yulia Skripal in Salisbury.

“The only thing the Russians respond to is determination and firmness,” Mr. Johnson advises him.

He said the UK is “like almost 100 per cent sure” that Russia committed the attack, adding: “We will be able to do more to illustrate that… We will continue to tighten the squeeze on some of the oligarchs who surround Putin.

“You throw a stone in Kensington and you’ll hit an oligarch. But some of them are close to Putin and some of them aren’t.”

“We will continue to tighten the squeeze on some of the oligarchs who surround Putin,” he also says, discussing the UK government’s crackdown on Russian money in London.

A Foreign Office spokesman confirmed the call took place, saying: “The foreign secretary realised 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.

“These childish actions show the lack of seriousness of the caller and those behind him.”