The Kremlin on Tuesday repeated its position that Russia was open to negotiations to end the Ukraine conflict, but that new "territorial realities" could not be ignored.

Kremlin spokesman Dmitry Peskov told reporters Russia would never renounce its claims to four Ukrainian regions that Moscow declared it had annexed last year following referendums that Kyiv and the West slammed as bogus and illegal.

"There are certain realities that have already become an internal factor. I mean the new territories. The constitution of the Russian Federation exists, and cannot be ignored. Russia will never be able to compromise on this, these are important realities," Peskov said on Tuesday.

Russia proclaimed it had annexed the Donetsk, Luhansk, Kherson and Zaporizhzhia regions last September in a grand ceremony in Moscow.

The regions were subsequently named as constituent subjects of the Russian Federation in a constitutional decree.

Peskov said Russia was open to negotiations if Kyiv accepted Moscow's control over the regions.

"With a favorable state of affairs and the appropriate attitude from the Ukrainians, this can be resolved at the negotiating table. But the main thing is to achieve our goals," he said.

Russian forces do not fully control any of the four regions, and Moscow says it is fighting to "liberate" them from the control of Ukrainian neo-Nazis.

Kyiv and the West say this is a baseless pretext for an illegal land-grab.

Ukraine says Russian troops must leave every inch of its territory including the four annexed regions and the Crimean peninsula, which Moscow unilaterally annexed from Ukraine in 2014, before a peace plan can be discussed.