Ukraine’s State Security Service (SBU) has caught red-handed a Ukrainian working as a spy for Russia’s military intelligence agency, just days after a Ukrainian journalist was arrested on espionage charges in Russia.

The unnamed suspect had come to SBU’s attention after he offered a senior Ukrainian military official Russian citizenship and money in exchange for top secret documents on Ukraine’s military capabilities and work with foreign partners, it said on Sunday.

“He was caught by SBU officers red-handed while receiving a flash drive containing misinformation that he believed to be secret documents of a military nature,” a SBU statement said.

There was no immediate comment from Russian authorities.

On Monday, Russia’s FSB security service said it arrested a Ukrainian intelligence officer for gathering secret information on Russian defence and security bodies, a move that prompted Ukraine to warn its citizens against travelling to Russia.

Relations between the former allies are at an all-time low following Russia’s annexation of Ukraine’s Crimea peninsula in 2014 and support for pro-Russian separatists in the ensuing conflict that has killed over 9600 people.