The probe into the missing flight MH370 "remains a very difficult ongoing operation," Malaysian Prime Minister Najib Razak told his British counterpart David Cameron on Tuesday.

Najib made the remarks in a phone call with Cameron to discuss the investigation into missing flight MH370, a Downing Street spokesperson said.

Najib appreciated the support of the British Air Accidents Investigation Board and the satellite data provided by British satellite telecommunications company Inmarsat.

Cameron said his thoughts were particularly with the relatives of those on board, and would offer other support if required, the spokesperson added.

The two leaders agreed to keep in touch on the issue as necessary.