WASHINGTON (Reuters) - President Barack Obama urged President-elect Donald Trump on Wednesday to keep separate the issue of economic sanctions on Russia from the pursuit of talks to reduce nuclear stockpiles.

Trump, who takes office on Friday after winning the Nov. 8 election, said in an interview with the Times of London published on Monday that he would propose offering to end sanctions on Moscow in return for a nuclear arms reduction deal.

Obama’s administration imposed the sanctions in 2014 after Russia’s annexation of the Crimea peninsula from Ukraine.

“Russia continues to occupy Ukrainian territory and meddle in Ukrainian affairs,” Obama told reporters during his final news conference at the White House.

“I think it would probably best serve, not only American interests, but also the interests of preserving international norms if we made sure that we don’t confuse why these sanctions have been imposed with a whole set of other issues,” he said.

“It is important for the United States to stand up for the basic principal that big countries don’t go around and invade and bully smaller countries,” the Democratic president added.

Trump, a Republican, has said he wants he wants to improve ties with Russia, despite allegations by U.S. intelligence agencies that Russian President Vladimir Putin ordered a cyber campaign to boost Trump’s campaign against Democrat Hillary Clinton. Moscow has denied the allegations.

Obama worked on a nuclear arms control agreement with Moscow early in his presidency, resulting in the Strategic Arms Reduction Treaty signed in 2010.

“I was prepared to go further, I told President Putin I was prepared to go further. They have been unwilling to negotiate,” Obama said, blaming Putin for “escalating anti-American rhetoric” and resuming what he called a Cold War-like “adversarial spirit.”

Obama said a more “constructive relationship” with Russia would be a good goal. The United States and Russia are by far the world’s biggest nuclear powers.

“If President-elect Trump is able to restart those talks in a serious way, I think there remains a lot of room for our two countries to reduce our stockpiles,” Obama said.