The Petrozavodsk phenomenon

A bright light sending pulsing rays to the ground, seen over Petrozavodsk at about 4 a.m. on 20 September 1977. Soviet researchers and James Oberg later tied it to a satellite launch from Plesetsk.

The first published report came from Nikolai Milov, a TASS correspondent, according to Wikipedia. He described "a huge star" that lit up the night sky over Petrozavodsk at about 4 a.m. local time and threw beams of light down to the ground. Pravda and Izvestiya carried his report, as did Sotsialisticheskaya Industriya and Selskaya Zhizn, and the local paper Leninskaya Pravda covered the object too. Yulii Platov and Boris Sokolov note that Izvestiya ran the story on 23 September 1977 as an unidentified natural phenomenon.

Russian Wikipedia says the Soviet press at the time offered a possible meteorite, or the remains of a satellite or rocket stage falling back through the atmosphere. It says the press gave no launch as the cause, because the authorities did not then officially admit that the Plesetsk cosmodrome existed.

In their 2000 history of Soviet state UFO research, published in Skeptical Briefs, Platov and Sokolov count the sighting among the most interesting cases caused by rockets and say it was eventually traced to Kosmos 955, a satellite launched from Plesetsk. James Oberg, writing in the MUFON UFO Journal in 1982, said his own research had proved it was a pre-dawn launch of the Cosmos-955 spy satellite from the secret base at Plesetsk. He also quoted an American who said Soviet UFO enthusiasts treated the case as their proof that UFOs are real.