The spokesman had no further details about the trip, but Hague tweeted overnight: "Have just spoken to Acting President (Oleksandr) Turchynov.
"I will travel to Kiev tomorrow for talks with the new government."
Turchynov had appealed to Russian President Vladimir Putin yesterday to "stop military provocation" and withdraw from Crimea, after pro-Russian gunmen seized the government and parliament buildings in the capital Simferopol.
A little earlier, British Prime Minister David Cameron had called Putin to stress the importance of respecting Ukraine's territorial integrity.