The Pentagon estimates that the NATO air campaign against Yugoslavia will cost the US three to four billion dollars, but the true costs will depend on the conflict's outcome, analysts say.
"If it goes to a ground war where the US and NATO are trying to forcibly evict Serbs from Kosovo or a larger ground operation trying not only to push Serbs out of Kosovo but push [Yugoslav President Slobodan] Milosevic out of power, then you could see costs getting much higher," said Dr Steve Kosiak, of the Centre for Strategic and Budgetary Assessments. "At the extreme end, add five to ten billion more to the operation," he said.
Dr Kosiak said Operation Allied Force is still "far cheaper" than Operation Desert Storm, the 1991 air and ground war to liberate Kuwait, which cost the US $60 billion (£43.7 billion). His organisation, which monitors US defence budgets, estimates that the 22-day-old air campaign has cost $400 million to $600 million so far.
"If you continue the air campaign through the end of the month at the more intensive level they're planning with 300 additional US aircraft, you could have cost of one to two billion by end of the month," he said. "On top of that if you assume 5,000 army troops to support Apaches [the attack helicopters being prepared for combat] through September that could be another billion dollars." he said.
If the operation ends successfully, said Dr Kosiak, at least 4,000 US troops and possibly more will deploy as part of an international peacekeeping force - an additional cost.
The Pentagon says it intends to ask Congress to fund the operation as a supplement to the $250 billion US defence budget for the fiscal year 1999. Congressional leaders have indicated it will be quickly approved.
The British Chancellor, Mr Gordon Brown, yesterday assured MPs that Britain could afford to pay for the Balkans conflict. During Commons questions, Mr Brown told Labour's Mr Tam Dalyell that Labour prudence had reduced the national debt, allowing emergencies to be funded from reserves.
Defence expert Mr Paul Beaver, of Jane's Information Group estimated Britain's share to be mounting at a rate of about £1 million a day.