UK military operations in Libya could cost about £260m over six months, the defence secretary has said.
In a written statement to MPs, Liam Fox said that if the Nato-led mission lasted that long, costs would be "in the region of £120m".
He added that up to £140m would also be spent replacing munitions.
The UK has been contributing to the operation to enforce a no-fly zone since 19 March. Overall costs will be met by Treasury reserves.
Earlier, Dr Fox said avoiding civilian casualties drove up costs but the spending showed the UK held the "higher moral ground".
When military strikes against Col Muammar Gaddafi's forces began, Chancellor George Osborne estimated that the cost of British involvement would be "in the order of tens of millions of pounds, not hundreds of millions".
But last week, Treasury Chief Secretary Danny Alexander said the cost could run into "hundreds of millions" of pounds.
Valuing human life
Ahead of his announcement, Dr Fox people would "have to take into account that we have used more expensive precision weaponry so that we minimise civilian casualties in Libya.
"And if we are going to fight operations in the future based on minimising civilian casualties, there is clearly a financial price to pay."
He added: "I think that shows that we are on the moral high ground and that we place a higher value on human life than the Gaddafi regime."
Shadow defence secretary Jim Murphy said Nato allies had to do more to reduce the British contribution.
He said: "Many people at home will be thinking 'Why is it always Britain that has to do this?' and I think it is important that Britain does contribute, but I think we want to see some more of our Nato allies, particularly the European Nato allies, do more of the campaign [and] more of the fighting."
In a later statement, Mr Murphy added: "We want the government to be clearer on what stresses and strains operations in Libya are making on the core defence budget, and whether our standing commitments are, or will be, affected by the ongoing conflict."
Pressed by shadow chancellor Ed Balls about the issue of costs during Treasury questions in the Commons on Tuesday, Mr Osborne said the cost was being met by the Treasury special reserve and was "very much lower than the ongoing operation in Afghanistan".
Earlier this week Air Chief Marshal Sir Simon Bryant, the RAF's second-in-command, said morale among RAF personnel was "fragile" and their fighting spirit was being threatened by being over-worked because of operations in Libya.
But Prime Minister David Cameron said on Tuesday that military leaders were "absolutely clear" the mission could be kept going for as long as necessary.