Washington (AFP) - The White House said Monday it rejects Russia's annexation of the Crimean Peninsula from Ukraine in 2014, and US sanctions will remain in place until the move is reversed.

"We do not recognize Russia's attempt to annex Crimea. We agree to disagree and the sanctions against Russia remain in place until Russia returns the peninsula to the Ukraine," White House spokeswoman Sarah Sanders told reporters.

Trump, who is due to meet his Russian counterpart Vladimir Putin on July 16 in Helsinki, was vague on the issue when pressed by reporters Friday.

"We're going to have to see," he said.

The Kremlin said Putin and Trump can discuss "all other issues" except Crimea.

Putin has "repeatedly stated and explained that Crimea cannot be and will never be on the agenda because it is an inseparable part of Russia," Kremlin spokesman Dmitry Peskov told reporters.

Accepting that Crimea is never to return to Ukrainian control would be a major concession to Russia, which is languishing under tough international trade sanctions over its actions.

In early 2014, with areas of Ukraine falling into chaos in the wake of a Kiev street revolt that ousted a pro-Russian president, Russian troops -- in unmarked uniforms -- seized Crimea.

A referendum was called in the territory, which has a large Russian-speaking population, and on March 18, 2014 Russia formally annexed it to the Russian federation.

Ukraine, which is also facing a pro-Russian rebellion on its mainland in the Donbas region, furiously opposed this breach of its sovereignty -- with stern Western backing.