Australia says the search for the missing Malaysia Airlines flight MH370 will focus on the southern part of the search area in the Indian Ocean.
Officials said further refinement of satellite data found the plane may have turned south earlier than thought.
The announcement came as Australia and Malaysia signed an agreement on the search's next phase, which will see the two countries sharing costs.
Based on analysis of satellite data, it is believed to have ended its journey in seas far west of the Australian city of Perth.
Investigators do not know what happened to the flight and finding its "black box" flight recorders is seen as key to understanding the factors behind its disappearance.
'Interest and priority'
Australia, which is responsible for search and rescue operations, has been looking for the plane in an area about 1,800km off its west coast.
The latest detail on the plane's possible flight path came from an analysis of a failed attempted satellite phone call from Malaysia Airlines to the plane, said Australia's Deputy Prime Minister Warren Truss.
"The search area remains the same, but some of the information that we now have suggests to us that areas a little further to the south... are of particular interest and priority," he told reporters in Canberra.
A Dutch contractor, Fugro Survey, will kick off the next phase in the search in September. Three vessels towing underwater vehicles will scan for the plane.
The search will focus on an area of about 60,000 sq km and is estimated to cost about A$52m (£29m, $49m).
Malaysia's Transport Minister Liow Tiong Lai signed the memorandum of understanding with Truss.
The two were also briefed on search efforts, together with China's Transport Vice-Minister He Jianzhong.
Most of the passengers onboard the flight were Chinese. The ministers issued a statement saying they "remain cautiously optimistic" that the plane will be found.