(Reuters) - The European Union will hold Moscow accountable for the "unjustified" attack on Ukraine, the chief of the bloc's Executive Commission, Ursula von der Leyen, said on Thursday.

       "In these dark hours, our thoughts are with Ukraine and the innocent women, men and children as they face this unprovoked attack and fear for their lives," she said on Twitter.

       "We will hold the Kremlin accountable," von der Leyen added.

       EU leaders are set to hold an emergency summit in Brussels later on Thursday, after a first round of EU sanctions on Russia took effect on Wednesday.

       (Reporting by Sabine Siebold; Editing by Clarence Fernandez)