White House national security adviser John Bolton says that he has discussed Russia’s illegal annexation of Crimea with Russian President Vladimir Putin.

Bolton, who met with Putin in Moscow on June 27, told CBS's Face The Nation that "President Putin was pretty clear with me about it and my response was we're going to have to agree to disagree on Ukraine.”

Putin and U.S. President Donald Trump are scheduled to hold their first one-on-one summit in Helsinki on July 16.

On June 29, Trump declined to rule out recognizing Russia's 2014 annexation of Ukraine's Crimean Peninsula.

Asked by reporters on Air Force One whether reports about him dropping Washington's longstanding opposition to the annexation were true, Trump said, "We're going to have to see."

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Trump gave a similar answer when asked whether he would consider lifting U.S. sanctions on Russia that were imposed over the annexation.

He has said the goal of his upcoming summit is to improve Washington-Moscow relations, which are at a post-Cold War low.

"We'll see what Russia does," Trump said.

Bolton ruled out the possibility of abandoning Washington’s opposition to the annexation. “That’s not the position of the United States,” he told CBS on July 1.

"I think the president often says 'we'll see' to show that he's willing to talk to foreign leaders about a range of issues and hear their perspective,” Bolton said.

Russian Foreign Minister Sergei Lavrov said in an interview on June 29 that Putin will not raise the issue of sanctions in his meeting with Trump, although he added that Russia "would not mind" if Trump chose to lift them.

The European Union and United States originally imposed the sanctions to penalize Russia for its illegal annexation of Crimea in 2014 and its backing of separatists fighting against the Ukrainian government forces in eastern Ukraine.

The sanctions have been in place since that time. On June 29, EU leaders extended their sanctions against Russia's banking and energy sector for another six months until the end of January.

Based on reporting by Reuters and The Washington Post