Britain’s top diplomat flew Wednesday to Moscow, seeking to defuse tensions raised by Russia’s military buildup near Ukraine and warning that an invasion would bring “massive consequences for all involved.”

“Russia has a choice here. We strongly encourage them to engage, de-escalate and choose the path of diplomacy,” Foreign Secretary Liz Truss said ahead of departing on the first visit to Moscow by the U.K.’s top envoy in more than four years.