President-elect Donald Trump has avoided saying who he trusts more — German Chancellor Angela Merkel, a longtime US-ally, or Russian President Vladimir Putin.

“Well, I start off trusting both — but let’s see how long that lasts," the incoming president said in an interview with The Sunday Times.

"It may not last long at all.”

During the interview, Mr Trump said Britain's decision to leave the EU would "end up being a great thing" and reiterated his claim Nato is "obsolete because it wasn't taking care of terror".

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Mr Trump also criticised Ms Merkel's immigration policies.

Despite saying he had "great respect" for the German leader, Mr Trump said she had made a "catastrophic mistake" by welcoming an unlimited number of refugees to her country.

He also suggested the December Christmas market attack by a Tunisian man was one effect of Ms Merkel's policies.

The President-elect said he will consider reviewing sanctions against Russia if Mr Putin is prepared to move away from confrontation with the US.

"For one thing, I think nuclear weapons should be way down and reduced very substantially, that’s part of it," he said.

"But Russia’s hurting very badly right now because of sanctions, but I think something can happen that a lot of people are gonna benefit."

Trump's message to Putin

Breaking with his previous rhetoric, Mr Trump condemned Russia's involvement in the Syrian conflict.

He said: “It’s a very bad thing, we had a chance to do something when we had the line in the sand and... nothing happened.

He added: "Aleppo was nasty. I mean when you see them shooting old ladies walking out of town — they can’t even walk and they’re shooting ’em — it almost looks like they’re shooting ’em for sport — ah no, that’s... a terrible situation.”

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Mr Trump also took aim at another key western alliance in the interview, saying Nato has not reformed to meet the main threat of Islamist terrorism.

He called the North American Treaty Organisation "obsolete because it wasn't taking care of terror" and said member organisations are not paying their "fair share".

“I said a long time ago that Nato had problems. Number one it was obsolete, because it was designed many, many years ago. Number two the countries aren’t paying what they’re supposed to pay."