Russia will “respond” if Russian citizens start being killed anywhere, including in Ukraine’s rebel Donbass region, Russia‘s RIA news agency cited Russian envoy to the European Union, Vladimir Chizhov, as saying on Tuesday.

“We will not invade Ukraine unless we are provoked to do that,” Chizhov said. “If the Ukrainians launch an attack against Russia, you shouldn’t be surprised if we counterattack. Or, if they start blatantly killing Russian citizens anywhere – Donbass or wherever.”

The Moscow-backed rebels say the Kyiv government is preparing an offensive against them, while Ukraine says Russia, which has amassed over 100,000 troops close to Ukrainian borders, is planning to invade its neighbour.

British Prime Minister Boris Johnson and U.S. President Joe Biden on Monday agreed in a call on Monday that there was a crucial window for diplomacy, but Truss said an invasion could be imminent, and Russian troops could reach Kyiv “very, very quickly.”

“This is … about the wider stability of Europe,” she told Sky News. “And it’s about wider global stability, and the message that we give to aggressors and we have to give the message to Vladimir Putin that there can be no reward for aggression.”

Truss echoed politicians in the United States who have warned that a so-called “false flag” operation could be used by Moscow to trigger a conflict.

“It is still the case that an invasion could be imminent, and it is highly likely,” she said.