From his speaker's chair in parliament, acting president Oleksander Turchinov referred to three deaths in two days in Donetsk and Kharkiv and said there was "a real danger" of invasion by Russian troops across Ukraine's eastern border.
Addressing members of the party of the pro-Moscow president who was ousted in last month's Kiev uprising, Turchinov said: "You know as well as we do who is organising mass protests in eastern Ukraine - it is Kremlin agents who are organising and funding them, who are causing people to be murdered."
Two men, described by police as pro-Russian demonstrators, were shot dead in a fight in Kharkiv late on Friday. A Ukrainian nationalist was stabbed to death when pro-Russia and pro-Ukraine demonstrators clashed in Donetsk on Thursday.
Turchinov, quoted by local media, closed the parliamentary session by saying: "The situation is very dangerous. I'm not exaggerating. There is a real danger from threats of invasion of Ukrainian territory and we will reconvene on Monday at 10."