A British trawler has been seized by France and another has been given a verbal warning, amid an escalating row over post-Brexit fishing rights, BBC News reported. 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". Girardin said on Twitter one of the British trawlers was caught fishing in the Bay of Seine without the proper licenses. 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. Meanwhile, the other boat was cautioned for initially resisting the check, 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 licenses was not resolved by 2 November. 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 licenses 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, including: Preventing British fishing boats from disembarking at ports; Increasing border and sanitary checks on UK goods; Tightening security checks on British boats; and Increasing checks on trucks going to and from the UK. France said it was also preparing further sanctions, which could include cutting electricity supplies to Jersey, a British Crown dependency, as it previously threatened in May. "The French state will continue to support its fisheries industry," the government said, adding that it expects answers from the UK "in the next few days". In a statement, Lord Frost said: "It is very disappointing that France has felt it necessary to make threats late this evening against the UK fishing industry and seemingly traders more broadly. "As we have had no formal communication from the French government on this matter we will be seeking urgent clarification of their plans. We will consider what further action is necessary in that light." Downing Street said on Wednesday the "disappointing and disproportionate" threat of sanctions was "not what we would expect from a close ally and partner". "The measures being threatened do not appear to be compatible with the Trade and Co-operation Agreement and wider international law, and, if carried through, will be met with an appropriate and calibrated response," a spokeswoman said. She said that the UK will raise concerns with both the EU and French government, arguing that it had granted 98% of license applications from European boats. The UK maintains the rejected applications which sparked the row did not have enough supporting evidence to show they had a history of fishing in Britain's or Jersey's waters.