The United States has spent US$608 million on its air war over Libya, US military officials said on Monday.

The figure covers the period from the start of international air strikes on Libya on March 19, to April 4, AFP reports. The previous cost amounted to US$550 million to March 28. Roughly 60% of this was for munitions while the remainder was for the ‘higher operating tempo’ of US forces, and included transport costs, AP reports.

The US military said its military operations over Libya will cost US$40 million a month, even though NATO has taken over the UN-mandated operation.

A US military official, who requested anonymity, said on Monday that the war cost the US Air Force roughly US$4 million a day. However, Air Force Secretary Michael Donley said the figure should come down as America’s European allies carry out most of the bombing raids while US aircraft play a supporting role, such as refuelling and reconnaissance.

The United States spent roughly US$55 million a day in the first ten days of operations, which then dropped to about US$8.3 million a day for the following week, Army Times reports.

The most recent US$608 million figure includes pay and other normal deployment costs, officials said on Monday. However, US Navy Commander Kathleen Kesler, a Defence Department spokeswoman, said it will take several weeks to tally exactly how much has been spent.