Ukrainian security services have detained two Russian soldiers near the border with Crimea, with Ukraine saying the men were deserters from the Ukrainian army detained on Ukrainian-controlled territory and Russia saying they were seized in Crimea.

Moscow and Kiev have been locked in conflict since Russia's annexation of the Crimean Peninsula from Ukraine in 2014, and an uprising by pro-Russian separatists in east Ukraine.

Russia's Defence Ministry said the Security Service of Ukraine (SBU) had detained the two soldiers at around 1 pm Moscow time on Sunday in Crimea and had taken them to Ukraine, according to Russian news agencies.

It demanded the two men's swift return to Russia, naming them as Maxim Odintsov and Alexander Baranov.

Ukraine's SBU told Interfax Ukraine that the men had been detained after crossing the border at Chonhar, and had served in the Ukrainian army before deserting to Russia.