Boris Johnson says there should be “no doubt” the only alternative to the Brexit proposals he will put to Brussels later is no-deal.
Addressing his party conference in Manchester, the PM said his plan would be a “compromise by the UK”, but he hoped the EU would “understand that and compromise in their turn”.
The European Commission said they will “examine [the proposals] objectively”.
The Irish PM said he had not seen the plans but was “not encouraged”.
Leo Varadker told the Irish Parliament: “What we are hearing is not encouraging and would not be the basis for agreement.”
The UK is set to leave the EU on 31 October.
The government has insisted it will not negotiate a further delay beyond the Halloween deadline, saying this would be unnecessary and costly for the UK.
However, under the terms of a law passed by Parliament last month, the PM faces having to request another extension unless MPs back the terms of withdrawal by 19 October – two days after a summit of European leaders.
The European Commission’s President Jean-Claude Juncker and Mr Johnson will speak on the phone later, and the two sides’ negotiating teams will also meet.
