French President Emmanuel Macron has placed any potential blame for a no-deal Brexit squarely at the feet of Britain, insisting that any trade pact between the UK and US would not redress the cost of such an outcome.

The French leader said the demands made by British Prime Minister Boris Johnson for a renegotiation of the divorce deal, including the removal of the Irish backstop, were not workable.

Macron laid out his concerns to reporters in Paris on Wednesday as German Chancellor Angela Merkel, in Berlin, gave Johnson 30 days to draw up an alternative solution to the backstop.

The backstop is an insurance policy to prevent the return of a hard border between Britain’s province of Northern Ireland and EU member Ireland.

‘‘Can the cost for Britain of a hard Brexit – because Britain will be the main victim – be offset by the United States of America? No. And even if it were a strategic choice it would be at the cost of a historic vassalisation of Britain,’’ Macron said.

‘‘I don’t think this is what Boris Johnson wants. I don’t think it is what the British people want.’’

A hard border on the island of Ireland would make a US-UK trade deal ‘‘highly unlikely’’, Johnson has been warned.

Today I travelled to Berlin to meet with Chancellor Merkel. This is a relationship that is so important for the UK, there are so many areas in which we work powerfully together. We in the UK want a deal and I believe that we can get one. 🇬🇧🇩🇪 pic.twitter.com/tbDgbhhuc6

— Boris Johnson (@BorisJohnson) August 21, 2019

The Congressional Friends of Ireland, a group in the US Congress which supports and promotes peace and reconciliation in Northern Ireland, has written to Boris Johnson warning that it will oppose any US-UK trade deal if it risks undermining the Good Friday Agreement.

The group said any trade deal between the UK and the US would be ‘‘highly unlikely’’ if the Good Friday agreement was in any way weakened.

This comes as German Chancellor Angela Merkel told Johnson he had 30 days to come up with an alternative solution to replace the backstop.

According to the letter: “The United States, and the more than 33 million Americans with Irish ancestry, share a genuine interest in the continued success of the Good Friday Agreement and the hard-won peace and prosperity it has brought to so many.

‘‘As you know, America is guarantor of that international peace accord.

‘‘That is why we strongly oppose any unravelling of the historic treaty or a return of a physical border on the island of Ireland under any circumstances.

‘‘We share the view expressed by other leaders in Congress that any weakening of the Good Friday Agreement or threat to the 310-mile seamless border would make the prospect of a future US-UK trade deal highly unlikely.’’

The letter raises concerns about the ‘‘tension-filled summer’’ in Northern Ireland, saying the peace process is ‘‘still fragile and needs to be nurtured’’.

It adds: ‘‘We will oppose any US-UK trade deal if the Good Friday Agreement is undermined.’’

Earlier on Wednesday, an official in Macron’s office said France now saw a no-deal as the most likely scenario come Britain’s October 31 deadline.

The official said there was not a ‘‘cigarette paper’’ standing between the positions of France, Germany and other EU states.

Macron said the possibility of a no-deal Brexit “would be Britain’s doing, always”.

‘‘The British are attached to being a great power, a member of the Security Council. The point can’t be to exit Europe and say ‘we’ll be stronger’, before in the end, becoming the junior partner of the United States, which are acting more and more hegemonically,’’ Macron added.

He said he saw no reason to grant a further delay to Brexit unless there was a significant political change in Britain, such as an election or a new referendum.

French officials say if Britain requested an extension in order to hold a new election, the EU would probably grant it.

Sticking to his previous hard line on Brexit, Macron said he would not accept renegotiating the withdrawal agreement agreed between Johnson’s predecessor and the bloc, and dropping the backstop.

‘‘Why won’t we accept it? It’s simple: because what Boris Johnson suggests in his letter to (EU) President (Donald) Tusk is … to choose between the integrity of the single market and respecting the Good Friday agreement.

‘‘We won’t chose between the two. We won’t jeopardise peace in Ireland, that would be one of the consequences of dropping the so-called backstop,’’ he said.

Ireland says border checks could undermine the 1998 Good Friday Agreement, which brought peace after more than 3600 died in a three-decade conflict between unionists who wanted Northern Ireland to remain British and Irish nationalists who want Northern Ireland to join a united Ireland ruled from Dublin.

The French leader will be hosting Johnson for lunch on Thursday.

-AAP