The U.K. cannot have an agreement without the Irish backstop, the European Parliament said on Thursday.

"You cannot have an agreement without backstop," David Sassoli, president of the European parliament, told a news conference, referring to a measure to avoid the reappearance of a "hard" border on Ireland.

"It couldn’t be any clearer. That is the position of European Commission, the position of the European institutions, including the European Parliament," he said. 

Sassoli said that the European Parliament has the "last word" on any kind of Brexit deal.

He added that the U.K has not proposed any alternatives to the withdrawal agreement.

British Prime Minister Boris Johnson has insisted that negotiations on a possible deal are continuing with EU officials.

"Up to now -- and I would like to stress this point -- the United Kingdom hasn't proposed any alternatives [to the backstop] and anything that has been legally credible," Sassoli said.

The president said if there is a no-deal departure, "it would be entirely the responsibility of the U.K."

He also said the EU would be open to extending the Brexit deadline from Oct. 31 to make room for a general election or to block a no-deal departure.

Britain's parliament has been prorogued since early Tuesday after the queen agreed to the suspension as requested by Johnson.

A Scottish court on Wednesday declared the suspension "unlawful," but the government said it would appeal the ruling at the Supreme Court next week.

The U.K. is set to leave the bloc at the end of October after two extensions granted by the EU.

Johnson has insisted that the country will leave with or without a deal on the date set.