CANBERRA, Australia — Relatives of some of the 239 passengers and crew on Malaysia Airlines Flight 370 want more of its possible debris to be examined to define a new search area for the missing plane.

The current search area in the southern Indian Ocean will be the last area thoroughly examined with deep-sea sonar equipment in the absence of credible new evidence that identified the plane’s location.

Eight relatives of lost passengers who met with Australian officials coordinating the search on behalf of Malaysia on Monday expressed frustration that what constituted credible new evidence has not been explained.

Some confirmed pieces of debris have washed ashore in the western Indian Ocean, and the families believe other items yet to be examined may be clues to the plane’s location.