Ukraine's security agency said it had uncovered, together with the FBI, a long-running Russian campaign to compromise the messaging accounts of government officials, military personnel, politicians and activists in Ukraine, Europe and the United States.

The campaign was aimed at gaining access to sensitive military, political and economic information exchanged through messaging applications, while also stealing victims' personal data, the Security Service of Ukraine (SBU) said in a statement on Thursday.

The attackers used a range of social engineering techniques rather than exploiting vulnerabilities in the messaging apps themselves, the SBU said. One of the most common methods involved sending text messages impersonating official messaging platform support services and urging users to disclose their account credentials.

"The messages are sent in the morning hours, when users are particularly vulnerable due to their physical and emotional state," the SBU said.

According to the agency, Russian intelligence services and affiliated hackers targeted government institutions, public officials, activists and ordinary Ukrainian citizens.

The SBU did not identify the Russian intelligence service responsible, specify which messaging platforms were primarily targeted or say how many victims had been affected. The FBI did not immediately respond to a request for comment.

The warning follows a series of disclosures by Ukraine and Western intelligence agencies about Russian efforts to compromise secure messaging platforms used by government and military personnel.

Earlier this year, Dutch intelligence agencies warned that Russian state-backed hackers were conducting a global campaign to hijack Signal and WhatsApp accounts belonging to government officials, diplomats and military personnel.

The attackers typically posed as customer support workers to trick victims into sharing one-time verification codes or PINs.

Ukraine has previously reported Russian espionage operations targeting messaging applications used by its military, including campaigns involving data-stealing malware and attempts to extract encrypted Telegram and Signal communications from mobile phones captured on the battlefield.