Russia said it would not return the Crimea region to Ukraine and stressed the territory was not being occupied by Russia, almost a year after Moscow annexed the Black Sea peninsula after an internationally condemned referendum.

The United States and the European Union have warned Russia that they will not drop sanctions related Russia's annexation of Crimea.

"There is not occupation of Crimea. Crimea is a region of the Russian Federation and of course the subject of our regions is not up for discussion," said Kremlin spokesman Dmitry Peskov.

Russia seized the territory last February in the wake of the ouster of Ukrainian president Viktor Yanukovych, who fled the capital as nationwide protests turned violent.

Russia has defended its actions in Crimea, saying that it acted after a "coup" in Kiev in order to defend the rights of Russian-speaking residents of Crimea. The Russian annexation was completed after a discredited referendum on the peninsula and a vote in the Russian parliament.

US State Department spokeswoman Jen Psaki said the US would keep economic sanctions in place for as long as Russia retains control of Crimea.

The EU's foreign policy head Federica Mogherini echoed the sentiment, saying the bloc would not recognise the annexation of Crimea.

The Black Sea territory was previously given to Ukraine by Soviet leader Nikita Khrushchev after the second world war, although Russia had maintained a naval base on the peninsula.