In a statement published on the Telegram messaging app, SBU chief Vasyl Maliuk said the operation aimed to arrest the individuals, but they "offered armed resistance" and were "liquidated" during the raid.
Ukrainian police confirmed the deaths and said the individuals were of "foreign nationality," without specifying their country of origin.
The move follows the killing of Colonel Ivan Voronych, reportedly a high-ranking SBU officer, who was shot dead on Thursday in a car park in Kyiv.
Ukrainian media have widely identified the victim, though officials have not formally confirmed his identity.
According to the SBU, the suspects had been tracking Voronych's movements in the days prior to the assassination.
Ukrainian intelligence said the pair were provided with coordinates to a cache where they retrieved a pistol fitted with a suppressor.
Authorities said the suspects attempted to "lay low" after the attack, but were located through a joint SBU-police investigation.
The SBU did not specify how many agents were killed on Sunday but said the cell consisted of a man and a woman.
Russian authorities have not issued a comment on the incident.
The killing marks the latest in a series of covert actions linked to Russia's invasion of Ukraine.
The SBU, originally tasked with domestic intelligence and counterintelligence, has in recent years played a growing role in special operations targeting Russian military and intelligence assets.
(ał)
Source: IAR, Reuters