London council taxpayers have been warned there is no limit on the amount they may be expected to pay if the cost of staging the 2012 Olympics overruns.
Ms Jowell said they would work to contain the costs
But Culture Secretary Tessa Jowell told the culture, media and sport select committee that the costs for the Games had been planned with extreme "rigour".
Band D council taxpayers are expected to pay about £20 a year for 10 years to meet the cost of staging the Olympics.
Ms Jowell said there would be a "daily vigilance on monitoring the costs".
"What I cannot say is that there will be any guarantee there will be a cap," she added.
Ms Jowell said they would be "taking all reasonable steps available to contain these costs to the figures submitted in the candidate file".
Liberal Democrat London Assembly Olympics spokeswoman Dee Doocey said the announcement, so soon after winning the chance to host the Games, was "deeply concerning".
"It would be almost understandable if we were two or three years down the line..., but coming so soon after winning simply beggars belief.
"Why are ministers now sounding so pessimistic about whether the Games will be delivered on time and on budget? Londoners deserve an answer since they are set to bear a lot of the costs."
The council tax payer, the London Development Agency and the Lottery are contributing the public sector funding for the Games.
A spokesman for the department of culture, media and sport insisted they were "optimistic" the Games would come in on budget.
However, if spending went over budget, the extra costs would be met by the government and the mayor of London, said the spokesman.