It involved the frigate Admiral Grigorovich and a UK-registered yacht around 20 nautical miles south of the Isle of Wight just outside British waters, a UK defence source told AFP.

The Russian defence ministry said the shots were fired after the yacht named "Bright Future" appeared to be on a "dangerous course".

It came days after UK commandos intercepted and boarded a suspected Russian shadow fleet vessel in the same part of the Channel, in the first such UK-led operation.

The incident coincided with G7 leaders gathering in eastern France and agreeing Tuesday to intensify pressure on Russia to end more than four years of war against Ukraine.

Asked about the warning shots, a UK Ministry of Defence spokesperson said: "We are investigating reports of an incident in the Channel."

The defence source said it was being treated as an isolated case not linked to the UK interception in the early hours of Sunday.

"In order to attract the attention of the yacht's crew, signal flares were fired and audible signals were sounded. Despite these measures, the vessel continued its dangerous approach," the Russian defence ministry 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.

The UK-registered yacht alleged that the Russian vessel had fired the warning shots at a distance of approximately 500 yards (1,500 feet).

No injuries or damage was reported by the yacht, which is continuing its journey after a welfare visit by a seaboat dispatched from British naval vessel HMS Tyne.

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

Britain's Telegraph newspaper reported in May that the Grigorovich had been patrolling off the UK coast for almost two months, and was escorting tankers part of Russia's "shadow fleet" of sanctions-busting ships through the Channel.

The British navy previously said it had deployed multiple patrol ships to monitor the vessel, saying "there was not one day" in April that the frigate was not "closely watched".

It added that the Grigorovich had escorted Russian-flagged ships "heading to and from the Atlantic, Mediterranean and Baltic".

- Shadow vessel captain -

Sunday's interdiction saw British commandos board the sanctioned oil tanker Smyrtos -- said to belong to Russia's shadow fleet -- in a dramatic operation hailed by Kyiv and London as a blow to Moscow's war machine.

The operation took place off the southern English coast, with the commandos fast-roping from a helicopter in the dark, according to defence ministry footage released.

British prosecutors on Monday charged Ajay Pant, the Indian captain of the Smyrtos, with contravening UK sanctions imposed on Russia following its 2022 full-scale invasion of Ukraine.

The 38-year-old appeared Tuesday at Southampton Magistrates' Court by videolink from Bournemouth police station for a preliminary hearing.

He spoke only to confirm his name and date of birth, and to gave his address as being in India. He also gave no indication of his plea and his solicitor requested the case be sent to the crown court.

Pant was remanded in custody, ahead of a plea and trial preparation hearing at Bournemouth Crown Court on July 16.

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ADMIRAL GROUP