Russia's Defense Ministry says Ukrainian security services have arrested two Russian servicemen.

The ministry said Ukrainian agents whisked the two servicemen from Crimea into the Mykolaiv region Sunday. In Monday's statement, the ministry denounced the Ukrainian action as a "rude provocation" and demanded their immediate return.

Ukraine's security agency said, according to the Interfax news agency, that the two were detained on the border with Crimea. It said they were former Ukrainian servicemen facing accusations of treason.

Russia-Ukraine relations are at freezing point after Russia's annexation of Ukraine's Crimean Peninsula and support for pro-Russian insurgents in eastern Ukraine.

Earlier this month, Russia's Federal Security Service reported the arrest of several Ukrainian citizens in Crimea who were accused of plotting acts of sabotage. Ukrainian officials have rejected the accusations.