The regions listed in the FCO's travel advice include Kharkiv, Donetsk and Lugansk in eastern Ukraine. Meanwhile, the FCO continued to advise against "all travel to Crimea", and advised any British nationals remaining in Crimea to leave, Xinhua reported.
"The FCO is not able to provide consular services to anyone choosing to remain in Crimea. Events in Ukraine are fast moving," the alert said.
"Travel advice for the rest of Ukraine remains unchanged, but we continue to advise all British nationals to take great care and remain vigilant in all parts of the country," it continued.
The flights in and out of Simferopol airport are "subject to disruption," and Ukrainian International Airlines have cancelled all flights to and from Simferopol until April 29, the advice said.