The EU has accused Jersey of breaching the terms of the UK’s post-Brexit trade deal in the bitter stand-off over fishing rights in the Channel island’s waters.

The European Commission complained the authorities were imposing “additional conditions” on French fishing boats operating there, in breach of the terms of the agreement hammered out on Christmas Eve.

But in a call with Jersey’s chief minister John Le Fondre, Boris Johnson again voiced his “unequivocal support” for the actions taken by the island’s government.

He said two Royal Navy patrol boats despatched to the area on Wednesday would remain in place as a “precautionary measure”.

Around 60 French fishing boats gathered off the island’s main port St Helier early on Thursday to protest against the new licences they have been required to obtain from the Jersey government to carry on operating.

Local fishermen reported flares were let off and that some boats entered the harbour for around an hour, with footage posted online apparently showing a French boat ramming the rear of a Jersey vessel.

The French maritime authority for the Channel sent a pair of police patrol boats to the area “to ensure the protection of human life at sea”.

The protest leaders denied they were seeking to impose a blockade and the flotilla eventually headed back to France.

In an attempt to defuse the row, representatives of the Jersey government met the fishermen, with their boat pulling alongside one of the French vessels so they could talk ship-to-ship while observing Covid restrictions.

External relations minister Ian Gorst said the discussions were “positive” but some of the fishermen were reported to be unhappy, complaining there had been little progress.

The row erupted after the Jersey government said French boats would be required to obtain licences to carry on fishing in the island’s waters under the terms of the trade deal with the EU which came into force last Friday.

The move provoked a wave of anger among French fishing communities who complained that boats which had operated there for years were suddenly having their access restricted, because they could not prove their historical links with the waters.

In Brussels, a spokeswoman for the European Commission said “additional conditions” attached to the new licences represented a breach of the trade deal.

She said they had “indicated to the UK that we see that the provisions of the EU/UK Trade and Co-operation Agreement, that we recently agreed, have not been met there, have not been respected”.

Mr Gorst said the Jersey authorities were “extremely grateful” to the UK Government for its prompt deployment of the patrol boats HMS Severn and HMS Tamar following warnings French fishing boats could try to mount a blockade.

However he insisted that they wanted to find a diplomatic solution to de-escalate the situation.

“It’s important that we respond to threats, but the answer to this solution is to continue to talk and diplomacy,” he told BBC News.

Earlier this week, French maritime minister Annick Girardin said Paris would cut off electricity to Jersey – which gets 95% of its power supply from France – if the dispute was not resolved.

The Jersey government has said that of the 41 French boats that applied for licences last Friday, 17 had been unable to provide the evidence needed to enable them to carry on as before.

Mr Gorst said: “It’s really important that we are able to work with those fishermen to help them provide the necessary evidence so that, if required, their licences can be amended.”

Nevertheless, there was concern on the island that the French action could escalate if the dispute was not resolved.

Fisherman Josh Dearing said the appearance of the French boats had been “like an invasion”, and welcomed the presence of the Royal Navy ships.

“We’re completely unprotected in Jersey. We’ve got nothing except for a few police officers. We don’t have a police boat, we don’t have a navy boat, we don’t have anything to protect us,” he told the PA news agency.

“The French can be hostile. All of our livelihoods are in that harbour and if they wanted to they could cause damage.

“They can blockade their own harbours – they wouldn’t think twice about coming and doing it to us.”