Britain's Prime Minister Theresa May flies to Cardiff after visiting Scotland and Northern Ireland during a tour of the four nations of the United Kingdom exactly a year before it leaves the European Union, March 29, 2018. REUTERS/Stefan Rousseau/Pool

LONDON (Reuters) - Britain is looking for a “proportionate way” to respond to the threat posed by Russia, a spokesman for Prime Minister Theresa May said on Tuesday, after a retired Russian army official said the poisoning of a former spy could start a new world war.

“We need to respond in a proportionate way to this aggressive behavior from Russia and that’s what we’re doing,” the spokesman said when asked if there was a real risk of triggering a war.

Evgeny Buzhinsky, a retired lieutenant general, was quoted in British newspapers on Tuesday as saying the fallout of the attack could trigger “the last war in the history of mankind”.