The journalists from Russia's Zvezda, or Star channel -- Nikita Konashenkov and Yevgeny Davydov -- were detained yesterday by Ukraine's National Guard as they headed to the airport after covering the fighting in eastern Ukraine between government forces and pro-Russian rebels.
"The management of the channel appeals to Ukrainian president Petro Poroshenko to release (them)," the military broadcaster said in a statement.
The call followed a statement from Russia's foreign ministry late yesterday slamming Ukraine for "egregiously trampling on the rights of the Russian media."
Journalists have been targeted by all sides in the conflict during the nearly two months of bloodshed in the east, with Ukrainian and Western reporters also being held by pro-Russian rebels.
Ukrainian troops in May detained two Russian journalists from a pro-Kremlin website and television channel Life News in the same region, later claiming they were transporting anti-aircraft missiles in their cars.
The Life News reporters were freed a week later following the intervention of Chechen leader Ramzan Kadyrov. The Kremlin awarded the journalists medals for valour.