Warning shots fired by a Russian warship sailing across the Channel on Tuesday morning were “deeply concerning and reckless”, Keir Starmer said from the G7 summit on Wednesday as he warned that the UK was dealing with proxy attacks from Russia “every single day”.

The prime minister said the Ministry of Defence had assessed that the Russian vessel was drifting and fired the shots within a few hundred metres of a British pleasure yacht.

He said: “We’re living in a more volatile and dangerous world than we have at any time in our lifetimes … That is true, it’s not just an abstract description.”

The incident took place at 11.40am on Tuesday more than 20 miles south of the Isle of Wight and less than 40 miles north of Normandy, France, when the yacht, identified as the private vessel Bright Future, sailed close to the Admiral Grigorovich and ignored at least one warning.

British sources said initial indications were that Russian sailors fired more than one shot after the yacht had got close to the heavily armed frigate.

“Following attempts to contact a British vessel in the channel, the Grigorovich fired warning shots. These were not aimed at the vessel and were an attempt to prevent a possible collision,” the Ministry of Defence said.

Russia’s defence ministry said later the yacht was on a “dangerous course” and that several attempts were made to contact it. Signal rockets were fired, the Russians said, but the yacht continued to within 150 metres before a warning shot was fired.

Starmer told the BBC that the incident “shouldn’t have happened”, adding: “It is reckless, and the couple of the yacht must be terrified, and I think everybody will feel for them as I do.”

Asked about an arson attack on his house, Starmer said he wanted to keep the two incidents separate. Two men were found guilty of conspiring to carry out arson attacks on property connected to the prime minister on Monday and appear to have operated under the instruction of an online handler with links to Russia.

“In relation to the attack on our house, I’m very pleased that justice has been done, clearly, and as you would imagine it’s had an impact and affected my family,” Starmer said.

He said the world, including the UK, was dealing with an “aggressive” Russia. “We’re in the fifth year of the conflict in Ukraine, we’re discussing that here at the G7, and we know that both Russia and Iran are responsible for proxy attacks in the United Kingdom and across Europe, and we have to be alert to that,” he said.

“We’re dealing with that every single day, they take different forms, but that is the Russia that we are dealing with. That’s why it’s so important that an event like this here in France, the G7, where world leaders get together, we discuss the ways in which we address the Iran conflict, the Ukraine conflict, and also what we can do together for the resilience of all countries.”

Starmer, who vowed to “choke off” Russian revenue with further sanctions and to provide hundreds of millions of pounds’ worth of energy support for Ukraine at the G7 in Évian-les-Bains in France, said he was focused on the reopening the strait of Hormuz after a US-Iran ceasefire.

He was “equally focused” on supporting Ukraine to turn military pressure against the Russians “into the lasting peace that we all want in Ukraine”, he said.

‘“[It]will have a massive impact on our country, and I am really proud to have the United Kingdom here at the G7 seen as one of the leading countries in the huge debates on both of those issues.”