British Prime Minister Boris Johnson reacted Tuesday to the rejection by the European Union (EU) of his proposals for a new Brexit deal, amid mounting opposition from both EU and British parliament.

Brussels poured cold water on Johnson's suggestion in a letter to European Council President Donald Tusk that the controversial Irish border backstop proposal should be dropped by the EU as part of a Brexit deal.

Tusk tweeted on Tuesday that "the backstop is an insurance to avoid a hard border on the island of Ireland unless and until an alternative is found. Those against the backstop and not proposing realistic alternatives in fact support reestablishing a border. Even if they do not admit it."

In response, Johnson, in media interviews in Downing Street, described Brussels' reaction to his demand for the backstop to be scrapped as a bit negative, adding "but we will get there."

"I think there is a real sense now that something needs to be done with this backstop. We can't get it through Parliament as it is," he said.

Johnson said the EU must acknowledge the Brexit deal, brokered between former Prime Minister Theresa May and Brussels, had been summarily rejected by the British parliament.

The European Commission said Tuesday that Johnson's letter to Tusk did not contain a legally operational solution to prevent a hard border on the island of Ireland.

European Commission Spokeswoman Natasha Bertaud said the letter "does not set out what any alternative arrangements could be."

The European Parliament's Brexit spokesman, Guy Verhofstadt, echoed the comments made by the commission.

Verhofstadt said on Twitter that he did not see any majority in the European Parliament to remove the backstop.

"It is a vital insurance policy, negotiated in good faith and supported by the people of the island of Ireland. The time for bluster and political blame games is fast running out," he wrote.

British newspaper the Guardian said the EU had rebuffed Johnson's attempts to tear up the Irish backstop, in what was a coordinated response that appeared to close the door on further meaningful Brexit negotiations.

The newspaper added that as the standoff played out between London and Brussels, the British government confirmed that its officials would stop attending most EU meetings from Sept. 1, two full months before Britain leaves the bloc on Oct. 31.

The Brexit standoff is likely to set the stage for encounters between Johnson and German Chancellor Angela Merkel in Berlin on Wednesday, and between Johnson and French President Emmanuel Macron in Paris later this week. Johnson is expected to persuade both of them to agree that the EU should remove the backstop.

Meanwhile, a letter calling for the recall of the British parliament, in recess until Sept. 3, was handed to 10 Downing Street on Tuesday.

Labor MP Stephen Doughty, one of the parliamentary members who handed the letter addressed to Johnson, called it "a national emergency."

"There is no mandate for an undemocratic no-deal Brexit," Doughty said.