The Ukrainian Security Service (SBU) has detained a married couple suspected of spying for Russia in the Black Sea city of Odesa, one of Ukraine's largest ports.
An SBU statement issued on Thursday did not name the couple but accused them of collecting intelligence for Russia on locations for possible military deployments and the movement of air defence units.
It said the couple were believed to be Russian military intelligence officers who had planned to create a network of agents in southern Ukraine.
SBU officers found mobile phones and computer equipment with evidence of "hidden correspondence with the aggressor", it said.
"The SBU detained both spies when they attempted to transfer classified information to Russia," the SBU said.
The couple could not be reached for comment.
Odesa has frequently come under fire since Russia invaded Ukraine in February but it remains under Ukrainian control.
The SBU said both the man and woman detained had arrived in Ukraine in 2018 and received residence permits, and that the man had served in the Russian army.
It said the detainees had sent the information they collected to a former Russian special forces officer in Crimea who cooperated with military intelligence. The Crimea peninsula was seized by Russia in 2014.
The SBU also published a series of photos of the couple's arrest, the military documents of the detained man showing his military rank as colonel, as well as Russian passports of the detainees.
