The alleged plot to sell a surface-to-air missile to terrorists was foiled after multinational co-operation between the US, Russia and the UK.
Russia and the US have recently enjoyed close relations
Secret services in the three countries teamed up to monitor the route of the Igla missile bought in Russia and smuggled to the US.
The BBC reporter who revealed the plot, Tom Mangold, said this level of international co-operation was unprecedented and a "breakthrough".
And he said it was the result of decisions made at the G8 summit this year to stop the proliferation of missiles such as the Igla.
The sting began when Russia detected the arms dealer five months ago in St Petersburg and Moscow.
President Vladimir Putin, who has vowed to stamp out the illegal sales of arms, approved an FBI undercover agent be sent to Russia to work with his secret services, the FSB.
An FBI agent followed the British arms dealer on to a plane from London to New York and a new team of agents took up the surveillance in the US.
The man was arrested after collecting a package marked "medical supplies" - allegedly the deadly weapon in disguise.
MI6 and MI5 were also involved in gathering information, along with Scotland Yard officers, who are carrying out raids on addresses in London.
Tom Mangold said: "The key to all this is intelligence. If you don't know what's happening, if you can't get behind the scenes, if you can't work out what the plot is, then you may not be able to stop it.
"The great failure of 9/11 was that no-one had any intelligence to warn them about it."
The G8 summit in Evian, France, earlier this year, marked a new phase in international cooperation, he said.
"This is a very, very good start and it's old enemies now working together."