Boris Johnson has spoken out against Russian President Vladmir Putin's "lies" and inaction since Malaysian Airlines flight MH17 was shot down.
In a Telegraph column, the London Mayor, wrote: "This is his war. He bears responsibility, and he must not be allowed to get away with it. If he wants to prevent the reputation of Russia from being deeply and globally tainted, he must act fast: to secure the site for a proper international inquiry, to accept the truth of what has happened, and to cut off the rebels from further supplies."
He spoke out as the world continues to mourn the 298 passengers and crew - including 80 children - who lost their lives on board the Malaysian Airlines flight MH17, allegedly brought down by pro-Russian separatists.
Johnson made the huge distinction between Russia's defiant approach in accepting responsibility for the disaster to the US's handling of the Iranian passenger plane tragedy in 1988, which was blown out of the sky - killing all 290 passengers and crew. Naval warship, the USS Vincennes, was lying in the Straits of Hormuz at the height of the Iran-Iraq war - trying to keep the seas safe - when it mistook the Iranian civilian plane for a military aircraft.
"The first and most important difference was that when America erred, there was no significant attempt to deny the truth, or to cover up the enormity of what had happened, " Johnson said.
"An inquiry was held, and it was accepted that there was absolutely no fault on the side of the Iranian plane. It was concluded that the bridge crew had essentially made a disastrous error in thinking the plane looked hostile."
He said the US ended up paying the relatives of the victims of the Iranian disaster, $131.8 million, (£77.2 million) in compensatory damages an international court settlement.
"In accepting some measure of responsiblity towards the bereaved, and in trying to get at the truth, the US showed a degree of maturity and wisdom. Contrast Putin, with his evasion and obfuscation and lies. Can you imagine him ever accepting the reality of what has happened, let alone doing something to atone, such as sending money to the families of the victims?"