UK Prime Minister Boris Johnson has told the EU the backstop plan for the Irish border must be removed because it is "unviable" and "anti-democratic", - BBC has reported.
In a letter to European Council President Donald Tusk, the PM said the backstop - which aims to avoid a hard border - risked undermining the Northern Irish peace process.
If the plan was removed, Mr Johnson claimed a Brexit deal would be passed by parliament.
In his letter, Mr Johnson described the arrangement as "inconsistent with the sovereignty of the UK" and insisted it could not form part of a withdrawal agreement.
The prime minister called for "flexible and creative solutions" and "alternative arrangements" - based on technology - to avoid a hard border.
He said the backstop should be replaced with a commitment to put in place such arrangements as far as possible before the end of the transition period - currently the end of 2020 under Mrs May's deal.
If they were not in place by the end of the transition period, Mr Johnson said the UK was "ready to look constructively and flexibly at what commitments might help".
"Time is very short. But the UK is ready to move quickly, and, given the degree of common ground already, I hope the EU will be ready to do likewise," he wrote.
"I am equally confident that Parliament would be able to act rapidly if we were able to reach a satisfactory agreement which did not contain the backstop."
In a phone conversation with Mr Johnson on Monday evening, Irish Taoiseach (prime minister) Leo Varadkar reiterated that the agreement could not be reopened and the backstop could not change.
The backstop - part of the withdrawal agreement - is an insurance policy to prevent a hard border in Northern Ireland. If implemented, it would see Northern Ireland stay aligned to some rules of the EU single market.