TEHRAN, June 29 (RIA Novosti) - Iran has released five British Embassy local members of staff, a day after eight of them were detained in Tehran on suspicion of being involved in post-election riots, state media reported.

Iran's state English-language Press TV said the release occurred after preliminary investigations were completed. The other embassy staff members are to remain in custody.

Police in Tehran arrested eight Iranian diplomats on Sunday, saying they were "inflaming post-election tensions in the country."

The IRNA official news agency quoted the Iranian intelligence minister as saying that the British Embassy had played a "crucial role" in the disturbances.

"The embassy sent its local staff to rallies," Gholam-Hossein Mohseni-Eje'I said.

U.K. Foreign Secretary David Miliband voiced concern on Sunday over the arrests of the embassy's Iranian employees, calling it "unacceptable."

President Mahmoud Ahmadinejad's landslide re-election sparked mass protests amid allegations of ballot fraud.

At least 13 people have been killed during election protests, according to Iranian media, and over 450 arrested in the largest challenge to the Islamic Revolution since the 1979 overthrow of the U.S.-backed shah.