Boris Johnson: US, UK Left 'Door Open' to Russia in Syria

The U.S. and Britain left the "door open" to Russia's intervention in Syria and its support of the regime of President Bashar al-Assad, British Foreign Secretary Boris Johnson said.

"If you look back at what happened in the last two or three years, you look back at the sequence of events in Syria, the decisions of my country, of your country, and not to intervene, look, there's no question. We left that door open, and I think we failed, somehow, to have the imagination to think that that was what Putin might do," Johnson said of Russian President Vladimir Putin in an exclusive interview with ABC News' George Stephanopoulos on "This Week."

"We've now got to deal with it," said Johnson, who prior to his appointment as Britain's top diplomat served as mayor of London and was a key supporter of the Brexit vote.

Putin's intervention in Syria shows "a spirit of assertiveness, a desire for Russia to have prestige on the world stage," Johnson said. "I've got no problem with people thinking the Kremlin is powerful if they use that power and influence to good ends ... And one way they can do that, right now, is tell Assad to stop the bombing in Aleppo. And they have the power to do this. They have the ability to make this happen."

With the recent collapse of a cease-fire in Syria that had been brokered by the United States and Russia, Johnson said it's vital that the U.S. and other powers continue talks, such as those Johnson participated in last week during the U.N. General Assembly in New York.

"I think it's vital that we continue to talk while there's any chance at all that the Russians can be persuaded to do the right thing by Syria and the world," he said.

Johnson also addressed criticism from comedian John Oliver and others that he is an odd choice for a diplomat, given his past colorful comments on foreign leaders. He's referred to President Obama's "part Kenyan" heritage, compared Hillary Clinton to a "sadistic nurse," and referred to Vladimir Putin as "Dobby the house elf."

Johnson said, "It's a chasm of shame and embarrassment and the gaffes. First of all, all those little nuggets are taken out of context, many of them, actually, in a satirical sense."

"Number two, actually, the amazing thing is people are not so interested," Johnson said. And no one, he said, has asked him for an apology.