A section of the Druzhba oil pipeline in Ukraine has been partially suspended, Russia's TASS news agency reported on Wednesday, citing the state-owned pipeline operator Transneft.

It was not immediately clear what caused the partial suspension. It came as Russia rained down missiles across Ukraine, forcing shutdowns of nuclear power plants and triggering electricity cut offs even across the border in Moldova.

"The oil pipeline in Ukraine has been partially stopped, according to our partners," TASS cited Transneft spokesman Igor Dyomin as saying. The oil flow to Hungary, which has been suspended for three days, was likely to remain so for a week, he added.

Hungarian oil and gas group MOL did not reply to a Reuters request for comment.

Flows to the Czech Republic and Slovakia - which branch off just inside Ukraine from the pipeline heading further south into Hungary - were continuing, as was pumping from Belarus towards Ukraine, TASS reported.

Ukraine state oil pipeline company UkrTransNafta and the Ukrainian Energy Ministry were not immediately available for comment. The ministry said earlier on its Facebook page that the missile strikes had cut off power for "the vast majority of electricity consumers across the country."