Chancellor John Healey has told MPs that the government is "behind" a third runway at Heathrow Airport, but Prime Minister Andy Burnham has declined to back the same position.
Mr Healey set out his support for the project on Wednesday when he appeared before the Treasury select committee.
Chancellor's comments to MPs
Asked what assessment the Treasury had made of the economic benefits of a third runway, and how quickly those might materialise, Mr Healey told the committee: "So the government is behind a third runway at Heathrow, I'm part of the government.
"Our experience in recent decades, is it not, is that successful airports are very often an engine for economic growth in the wider area?
"That's as true in Manchester as it is true in parts of London and elsewhere.
"In terms of the assessment following the consultation period, that's not led by the Treasury.
"That's led by the Department for Transport, and the government is working through the responses and the further update information we've got from that."
Prime minister's response
Mr Burnham, who has repeatedly refused to back proposals for a third runway, failed to endorse the Chancellor's remarks.
The Prime Minister said he could not "pre-judge" a consultation into the airport's expansion, when asked whether he supported Mr Healey's comments.
He told reporters during a Thursday trip to the European Political Community summit in Dublin: "Well, there's a consultation that has been taking place.
"Obviously looking at all the replies, there is a process under way within government where a final decision will be taken, and I can't pre-judge it."
Before Mr Burnham entered No 10, his predecessor Sir Keir Starmer and then-chancellor Rachel Reeves had backed the construction of a third runway at the UK's busiest airport.
Background and concerns
Proponents highlight the major potential economic benefits from expanding the transport hub.
Concerns have been raised about the environmental impact, and about the potential effect on people living near the airport to the west of London.