A British trawler has been seized by France and another one given a verbal warning, amid an escalating row over post-Brexit fishing rights.
French Maritime Minister Annick Girardin said the ships were cautioned during checks off Le Havre overnight.
She said the first did not comply right away and the second was not allowed to fish in French waters so was detained.
On Wednesday, Brexit Minister Lord Frost said French threats to block UK boats from ports were disappointing.
Ms Girardin said on Twitter one of the British trawlers was caught fishing in the Bay of Seine without the proper licences.
She said the boat was diverted to the port of Le Havre and detained by the judicial authority, where their catch could be confiscated and the boat held until a deposit is paid.
The boat’s captain also risks penal sanctions.
Meanwhile, the other boat was fined for initially resisting the check, Ms Girardin added.
The minister said checks on the British vessels were standard during the scallop fishing season.
But she added they had also been undertaken against the backdrop of the tightening of controls in the Channel, in the context of discussions on licenses with the United Kingdom and the European Commission.
France had warned that it would block British boats from some ports next week – as well as tightening checks on UK boats and trucks – if a post-Brexit dispute over fishing licences was not resolved by November, 2.
The UK said threats by France were “disproportionate” and a breach of international law and trade agreements.
Speaking before the latest development, Lord Frost said the government was seeking “urgent clarification” of France’s plans and would consider what further action is necessary in that light.
France was angered by a decision from the UK and Jersey last month to deny fishing licences to dozens of French boats, and argued that it breached the Brexit deal.
On Wednesday evening, it issued its ultimatum, saying it would begin to impose “targeted measures” from Tuesday of next week.
[More reports by BBC NEWS]