THE French president, Emmanuel Macron, has launched a scathing attack on Boris Johnson amid an escalating war of words over who shoulders the blame for the deaths of people attempting to cross the Channel.

Home Secretary Priti Patel had been due to meet with her counterpart in France, Gerald Darmanin, to discuss the crisis after 27 people died trying to cross the strait earlier this week.

However, a letter sent from Johnson to Macron, which the Prime Minister shared on Twitter, sparked a diplomatic dispute that led to the unilateral cancellation of that meeting.

In the letter, Johnson called on Macron to accept a bilateral agreement that “all illegal immigrants who cross the Channel” should be returned from the UK to France.

The letter, and Johnson’s sharing it on social media, was greeted with “surprise” in France.

Speaking to press, President Macron hit out at the British Prime Minister, saying he should not communicate through Twitter.

He also appeared to echo calls from Nicola Sturgeon to address the root causes of the refugee crises, ensuring that people don’t need to leave their homes at all.

Macron said: “If the matter was simple, it would have been solved. It isn't.

“For these women and men who leave poverty and struggle behind and try to reach the United Kingdom, they do not want to stay in France, they want to cross [the Channel] at all costs.

READ MORE: Priti Patel's stance on refugees shows she has not accepted the reality

“Therefore the proper answer lies in a serious cooperation in order to prevent those movements, to dismantle the trafficking rings and avoid those men and women arriving in our country [France] because it is already too late when they're here.

“I have talked with the Prime Minister a couple of days ago, in a serious manner, and I intend to keep working with all the countries and their leaders.

“I am surprised when methods are not serious. One does not communicate on those issues, from one leader to another, via tweets or by a letter made public. We are not whistle-blowers. Come on now.”

Macron closed by saying that they and other European nations would work with the British if they “decide to behave seriously”.

The National's translator said that Macron's tone was "gold" and described the speech as an expertly written "soft attack".

In a statement reported on French media, the Interior Ministry said the meeting on Sunday would go ahead with interior minister Gerald Darmanin and his counterparts from Belgium, the Netherlands and Germany and representatives of the European Commission.

A French government spokesperson said Johnson's letter did not "correspond at all” with discussions Johnson and Macron had when they spoke on Wednesday.

“We are sick of double-speak,” the spokesperson added.

The news follows the French foreign minister, Jean-Yves Le Drian, branding Boris Johnson a "populist who uses all elements at his disposal to blame others for problems he faces internally”.