MOSCOW, June 27 (Xinhua) -- Two people died and six others sustained poisoning injuries after being exposed to an unknown toxic substance at a birthday party in the Moscow region, the regional prosecutor's office said on Saturday.

Emergency services responded on Friday to a private property in the Solnechnogorsk district northwest of Moscow, where two men were found dead. Six others were hospitalized with signs of toxic poisoning, said the office.

According to TASS news agency, the partygoers had been drinking alcohol when an unidentified person offered them a white powdered substance. Investigators preliminarily identified the substance as mephedrone, and packets recovered at the scene have been sent for forensic examination.

The Moscow Region Prosecutor's Office said it is supervising the investigation, and drug ingestion is believed to be the primary cause of the fatalities. ■