Any Brexit backstop option that keeps the UK aligned with the EU customs union should only be in place for a "short time", Environment Secretary Michael Gove has said.
The Brexiteer said that by definition the fall-back position, a last resort if disagreements over plans for the Irish border are not resolved in time, was "a temporary infill".
He spoke after reports that last week's war cabinet meeting over Brexit discussed a plan under which the whole of Britain would observe EU external tariffs until the practical arrangements are in place to keep the Irish border open, potentially after 2020.
Pressed on how long the backstop time limit would be, Mr Gove told BBC Radio 4's Today programme: "It means what it says on the tin. That temporary means not permanent. It means for a short period of time.
"I'm not going to pre-empt the eventual position that we take after we have negotiated with the European Union and with Ireland."
He added: "The very nature of a backstop, everyone agrees, is that it should be a temporary infill to bridge the position.
"In the same way as when you move house, a bridging loan is meant to be temporary, but, whether that's weeks or months, we don't know precisely."
Ministers remain split over which plan for the Northern Ireland border to adopt.
Brexiteers including Foreign Secretary Boris Johnson support the "maximum facilitation" scheme - known as Max Fac - which would use trusted trader arrangements and technology like number plate recognition cameras to avoid the need for border checks.
Prime Minister Theresa May supports a "customs partnership" where the UK collects tariffs on behalf of the EU.
The backstop was devised as an alternative to the European Commission proposal that Northern Ireland should remain in the customs union if no better resolution for the border issue can be found.
This Brussels backstop was roundly rejected by Mrs May as something no British PM could sign up to, as it effectively draws a customs border down the Irish Sea.
Mrs May yesterday described the backstop as "a very limited set of circumstances for a limited time", adding: "Nobody wants this to be the solution that is achieved."
She spoke after Mr Johnson, on a visit to South America, had told Brexiteers they should not fear betrayal over the backstop.
He called on the Leave camp to give Theresa May "time and space" to negotiate a deal that delivers on her promise to take Britain out of the customs union and single market and enable it to strike new trade deals around the world.
But his comments will be seen as a thinly veiled warning to the Prime Minister that she must not let the so-called "backstop" become a permanent solution.