Grant Shapps was forced to abandon a visit to a port city in Ukraine after British intelligence warned of a credible missile threat from Russia.
Officials told the defence secretary Russia had become aware of his travel plans to Odesa, where a convoy carrying Volodymyr Zelenskyy and Greece’s prime minister had narrowly avoided an airstrike.
That news raised the threat level to Mr Shapps’s safety from substantial to critical, according to The Sunday Times, which had access to the delegation and was the first to report the abandoned plans.
Mr Shapps, travelling with chief of the defence staff Admiral Sir Tony Radakin and a small team of British officials, took an overnight train from Poland, arriving in Kyiv on 7 March.
But the planned onward journey to Odesa was called off after an intelligence update revealed the Kremlin’s knowledge of it.
“Putin has shown himself to be reckless, ruthless and careless,” Mr Shapps, who instead travelled back to the UK via Poland, told the Sunday Times.
“The fact that he came perilously close to essentially assassinating two Western leaders, it doesn’t matter whether that is deliberate or accidental.
“What the hell is he doing, and why the heck would the West allow him to do that kind of thing?”
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Five people were killed in the airstrike that just missed Mr Zelenskyy’s convoy, according to Ukrainian authorities, which happened on 6 March, the day before Mr Shapps arrived in Kyiv.
It was the senior Tory’s second trip to Ukraine as Defence Secretary and his third since the outbreak of the war in February 2022.
It comes as Mr Zelenskyy faces waning enthusiasm in the West for supporting Kyiv.
European countries are struggling to find enough weapons and ammunition to send to Ukraine, and US help worth $60bn (£47bn) is stalled over political differences in Washington.
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A Ministry of Defence spokesperson said: “On a recent trip to Ukraine, the defence secretary did not make a planned visit to Odesa for security reasons.
“The UK continues to provide strong support for Ukraine and the defence secretary’s visit and engagements only underscored the importance of this support in the face of Putin’s aggression.”