Boris Johnson has provoked a furious response from Russia after he said Moscow's forces may be guilty of war crimes in Syria.
The Foreign Secretary condemned the "barbaric" bombing of rebel held areas of Aleppo and accused President Vladimir Putin of "protracting" the conflict through his military support for the regime of Bashar al Assad.
The Russian Foreign Ministry hit back saying that if anyone was guilty of war crimes, it was British forces in Iraq.
Appearing on BBC1's The Andrew Marr Show, Mr Johnson said it was "the right question to ask" whether an air strike last week on a UN aid convoy - widely blamed on Russian warplanes - constituted a war crime.
"A war crime is defined as when you attack something, attack a civilian target in the knowledge that it is a civilian target," he said.
"Putin's regime is not only as it were handing Assad the revolver. He is in some instances actually firing the revolver himself. The Russians themselves are actually engaged.
"We have an absolutely tragic situation now in Aleppo which is being bombed and repeatedly bombed in a way that is absolutely barbaric. They (the Russians) are guilty of protracting this war and making it far more hideous.
"I think when it comes to instances such as the bombing of civilian apartments in Aleppo we should be looking at whether or not that targeting is done in the knowledge that those are wholly innocent, wholly innocent civilian targets. That is a war crime."
Russian Foreign Ministry spokeswoman Maria Zakharova retorted that Britain should look to its own record before criticising Russia.
"The foreign minister of Great Britain Boris Johnson said in a broadcast of the BBC that Russia is guilty of protracting civil war in Syria and, possibly, of committing war crimes in the form of air attacks on convoys with humanitarian aid," she said.
"All this is right except for two words: Instead of 'Russia' it needs to be 'Great Britain' and instead of 'Syria,' 'Iraq.'"
Mr Johnson joined the foreign ministers of the United States, France, Germany, Italy and the EU high representative in calling on Russia to take "extraordinary steps" to salvage Syria's shattered "cessation of hostilities" (CoH).
"The outrageous bombing of a humanitarian convoy, the Syrian regime's public denunciation of the CoH, continuing reports that the regime is using chemical weapons, and the unacceptable ongoing regime offensive on eastern Aleppo, supported by Russia, blatantly contradicts Russia's claim that it supports a diplomatic resolution," they said in a joint statement.