EU ambassadors are meeting to discuss what length of Brexit extension to offer the UK, as MPs consider Boris Johnson's call for an early election.
Most EU states are understood to favour a three-month delay, with an option to end earlier if a deal is ratified sooner than this by Parliament.
But France has argued for a shorter extension to the 31 October deadline.
The PM has said he will give MPs more time to debate his Brexit deal if they back a 12 December poll.
The government has said it plans to bring forward a Commons vote on an early general election on Monday if the EU offers a delay until 31 January.
Chancellor Sajid Javid admitted the government's pledge to deliver Brexit before the end of the month now "can't be met" because "everyone expects an extension".
He told BBC Breakfast the Budget on 6 November would also not be going ahead as planned because "what is more important right now, I think, is getting Brexit done and then having that general election".
But the chances of enough MPs backing the motion - which under the Fixed-Term Parliaments Act requires the support of two-thirds of MPs - appear uncertain, with Labour not committing to how it plans to vote.
BBC
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