LONDON : UK Prime Minister Keir Starmer on Wednesday said a Russian warship's warning shots fired near a yacht in the English Channel were "reckless" but not "sinister", in the latest at-sea tension between London and Moscow.

British defence sources have told AFP that the incident involving a UK-registered yacht and the Russian frigate Admiral Grigorovich took place around 20 miles south of the Isle of Wight, just south of British waters, on Tuesday.

The Russian vessel fired the shots to avoid a collision, the British defence ministry has said, with a defence source telling AFP the frigate was believed to have been "drifting rather than being manoeuvred under power, which may have made her feel more vulnerable".

"I think it's reckless," Starmer said following the incident, which came after UK commandos intercepted and boarded a suspected Russian shadow fleet vessel on Sunday in the same part of the Channel.

But the Ministry of Defence assessment was that there was nothing "more sinister" about it, he told the GB News television channel.

That did not "take away from the fact that clearly Russia is aggressive across Europe", he added, however.

The incident came as G7 leaders gathered in eastern France and agreed Tuesday to intensify pressure on Russia to end more than four years of war against Ukraine.

Moscow said earlier the frigate fired the shots after the UK-registered yacht made a "dangerous approach".

"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 UK defence ministry said.

The ministry insisted that it was an "isolated" incident not linked to the UK's weekend interception of the other vessel.

- 'Surreal' -

The Russian defence ministry said "signal flares were fired and audible signals were sounded" to get the attention of the yacht on Tuesday.

"Despite these measures, the vessel continued its dangerous approach," Moscow said in a statement.

Following this, "the frigate's commander decided to fire warning shots in the vessel's direction using the ship's small arms", it added.

A British retired couple who were aboard the yacht, Jane and Alan Kelvey, described the experience as "surreal" in an interview with the BBC.

Jane Kelvey said the warship blasted its horn five times, before the couple "immediately turned two degrees to port so they could see we had made a deliberate change of course, which meant we had seen them".

"Then a minute or so later they gave another five blasts on their horn, immediately followed by four to five small arms fire," she said.

"That wasn't aimed at us -- it was warning fire that went up in the air, we believe."

She said their vessel was not on a collision course, disputing the Russian allegation that the yacht was on a "dangerous" approach.

Alan Kelvey said the gunfire was "unnecessary".

The UK-registered yacht alleged that the Russian vessel had fired the warning shots at a distance of approximately 500 yards (450 metres).

No injuries or damage was reported by the yacht, which was continuing its journey.

- Russia 'baring teeth' -

Steve Prest, an associate fellow at the RUSI think tank and retired British navy commodore, said the warning shots could have been the warship "getting a bit nervous".

"However, in the context of what's been going on with the (Russian) Dark Fleet, the Royal Marines seizing that ship, I think this is the Russians baring their teeth," he said in written comments shared with AFP.

Labour MP Tan Dhesi, head of the parliamentary defence committee, warned that delays in defence investment, and the resignation on Thursday of UK defence minister John Healey over a spending row, "have slowed us down at a time when we need to invest in defence".

It is understood another British naval vessel, HMS Mersey, was monitoring the Russian ship at the time.

The UK's Royal Navy said it had deployed multiple patrol ships in April to monitor the Grigorovich, which reportedly escorted tankers part of Russia's "shadow fleet" of sanctions-busting ships through the Channel.