WASHINGTON - US funding for the search and rescue operation for the missing Malaysia Airlines (MAS) flight MH370 will likely run out in April, said the Department of Defence (DOD).

"As of now, we've set aside US$4 million (S$5.1 million) to aid in the search," Pentagon spokesman Steve Warren told Xinhua news agency on Saturday.

"Based on our current expenditures, we expect these funds will last until sometime in the beginning of April."

The US has spent US$2.5 million on the mission so far, said Mr Warren, but adding that part of the costs would have been incurred even if the US was not roped in for the search. The USS Kidd destroyer, for example, "was already out and operating".

Mr Warren added that the number of flight hours and the deployment of any other assets could affect how fast the remaining fund runs out.

The US has offered two sophisticated military aircrafts, the P-8 Poseidon and P-3 Orion, for the search, which enters its 15th day.

Malaysia on Friday also requested the US to consider providing undersea surveillance equipment to step up the search.