Tavish Scott has told MSPs he is not prepared to write a blank cheque to pay for a new tramline in Edinburgh.
Trams disappeared from Edinburgh in the 1950s
However, the transport minister made the announcement as he pledged £93m to pay for interest accrued on costs since the line one project was planned.
It means there is still a £100m shortfall to reach the cost of building the route, which would run from Leith Waterfront to Edinburgh Airport.
The first section of the new line, could be up and running by 2010.
The transport minister welcomed the decision to build the line in sections, saying that recognised he "reality of the funding available at this time".
Mr Scott confirmed to MSPs on the Edinburgh Tram (Line One) Bill Committee that the Scottish Executive would index-link its contribution of £375m, taking it to somewhere in the region of £450 to £500m.
In addition Edinburgh City Council has already pledged £45m towards the cost of the project.
Council leaders had earlier told the committee one way in which future phases could be funded was by bidding for executive money.
But Mr Scott warned against councillors bidding for more money for the project in the near future.
He said: "I'm not prepared, and nor should I be prepared, to make any commitment to the future, that will probably be for a future transport minister at the stage where they get to that point."
But he added: "This is not a transport minister who is going to write an open chequebook or hold the chequebook in that way.
"This is someone who wants to make sure we get clarity about the numbers, we deliver what we say we're going to deliver and we do it in the timescale we've outlined."
Councillor Donald Anderson, leader of Edinburgh City Council, welcomed the executive decision to index-link funding for the tram project.