Britain's ongoing operations against Muammar Gaddafi have cost around £260 million, the Ministry of Defence has confirmed.
Defence secretary Liam Fox confirmed in a written statement to parliament that the net additional costs of military operations against Libya for six months would reach £120 million.
Based on current consumption rates, an extra £140 million will have to be spent on replenishing munitions, he added. The Treasury will meet the extra costs from its reserve.
Pressure to reveal the total bill for the UK's involvement in the international bid to put pressure on Colonel Gaddafi's regime had intensified amid growing concern about the conflict's longevity.
Chancellor George Osborne had told MPs in March that the cost of the Libyan intervention would be "in the order of tens of millions of pounds, not hundreds of millions".
But earlier this week chief secretary to the Treasury Danny Alexander admitted the conflict was costing "hundreds of millions".
"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," shadow defence secretary Jim Murphy commented.
"Being clear on the endgame – how and when our forces will return home – must be the government's priority."
Senior military figures have voiced doubts about Britain's ability to continue Operation Ellamy, Britain's part of implementing the no-fly zone over the skies of Libya.
David Cameron hit back at yesterday's PMQs, warning his military colleagues to "think very carefully about what you're about to say". He insisted that "time is on our side" and added: "I believe we'll take it to a satisfactory conclusion."
Earlier this week he told the military's top brass: "You do the fighting and I'll do the talking." Labour leader Ed Miliband told him his approach was "crass and high-handed".
Mr Osborne and shadow chancellor Ed Balls clashed over the Libya budget in Treasury questions earlier this week.
Complaining about the lack of an immediate answer to the budget question, Mr Balls said: "It is about Treasury spending from the reserve, and it has a direct bearing on the national debt as well as on our national interests.
"Just a few weeks ago, the White House provided the US Congress with a 34-page document giving details of the costs up to June 3rd and the likely costs up to September."
Mr Osborne replied: "The costs come from the special reserve, as the right hon. gentleman well knows, and I can tell him that they are very much lower than those of the ongoing operations in Afghanistan."
He added: "I know that, when he was in the Treasury, everything was a Treasury matter, but in this government, we let the Ministry of Defence talk about defence operations."