Donald Trump, the US president-elect, has told a British newspaper that he will offer to end sanctions against Russia in return for a nuclear arms reduction deal with the Kremlin.

In an interview with The Times of London published late on Monday, Trump said he wanted nuclear weapons arsenals of the world's two biggest nuclear powers - the United States and Russia - to be "reduced very substantially".

"They have sanctions on Russia - let's see if we can make some good deals with Russia. For one thing, I think nuclear weapons should be way down and reduced very substantially, that's part of it," Trump was quoted by the newspaper as saying.

However, on December 22 Trump tweeted that the US must "greatly strengthen and expand its nuclear capability until the world comes to its senses regarding nukes". Around the same time, Russian leader Vladimir Putin also called for the strengthening of "strategic nuclear forces".

READ MORE: Dear Donald Trump - A letter from Russia

In Monday's interview, Trump said that the North Atlantic Treaty Organization (NATO), an alliance formed to counter the military power of the former USSR, has become obsolete.

NATO has not been "taking care of terror", he said.

Trump also criticised Russia for its intervention in the Syrian war, describing it as "a very bad thing" that had led to a "terrible humanitarian situation".

The interview was conducted by Michael Gove, a Conservative Party member and prominent Brexit campaigner who is known to be close to Rupert Murdoch, owner of Fox News.

In Moscow, members of parliament gave a mixed reaction to Trump's statement on the sanctions imposed by the Obama administration on Moscow over the Ukraine crisis.

Konstantin Kosachev, head of the upper house of parliament's international affairs committee, was cited by the RIA Novosti news agency as saying getting the sanctions annulled was not a goal in itself and not worth making security concessions.

But another Russian senator, Oleg Morozov, was quoted by the same agency as saying that Moscow would be ready to discuss the issue of nuclear cuts, something he said Russia itself favoured.

Russian connection

News of Trump's plan came as the outgoing US intelligence chief said that Trump lacks a full understanding of the threat Moscow poses to the US.

Director of Central Intelligence John Brennan's message on national television came five days before Trump becomes the nation's 45th president, amid lingering questions about Russia's role in the 2016 election.

"Now that he's going to have an opportunity to do something for our national security as opposed to talking and tweeting, he's going to have tremendous responsibility to make sure that US and national security interests are protected," Brennan said on Fox News, warning that the president-elect's impulsiveness could be dangerous.

"Spontaneity is not something that protects national security interests," Brennan said.

Questions about Trump's relationship with Russia have dominated the days leading up to his inauguration.

Retired General Michael Flynn, who is set to become Trump's national security adviser, has been in frequent contact with Russia's ambassador to the US in recent weeks, including on the day the Obama administration hit Moscow with sanctions in retaliation for the alleged election hacking, a senior US official said.

After initially denying the contact took place, Trump's team publicly acknowledged the conversations on Sunday.

"The conversations that took place at that time were not in any way related to the new US sanctions against Russia or the expulsion of diplomats," said Mike Pence, the incoming vice president, also in an appearance on Fox News.

The contact, as Obama imposed sanctions, raised questions about whether Trump's team discussed - or even helped shape - Russia's response.

Vladimir Putin, Russia's president, unexpectedly did not retaliate against the US for the sanctions or the expulsion of 35 Russian diplomats, a decision Trump quickly praised.

"Great move on delay (by V. Putin) - I always knew he was very smart!" Trump tweeted.

Trump has repeatedly called for a better relationship between the US and Putin's government.

"I think he has to be mindful that he does not have a full appreciation and understanding of what the implications are of going down that road," Brennan said.