Australian officials said that two new "ping" signals had been detected in the search for Malaysia Airlines Flight MH370, boosting confidence after more than a month of fruitless searching for the missing jetliner.
The signals, which could be from the plane's black box recorders, bring to four the number of overall "pings" detected in recent days within the search area by a US Navy "Towed Pinger Locator".
Angus Houston, head of the Australian agency co-ordinating the search, struck an optimistic tone when announcing the information, but urged caution as the task of searching the remote Indian Ocean region remained enormous.
"I believe we are searching in the right area but we need to visually identify aircraft wreckage before we can confirm with certainty that this is the final resting place of MH370," Mr Houston told reporters in Perth.
"I'm now optimistic that we will find the aircraft, or what is left of the aircraft, in the not too distant future," he added.
The black boxes record cockpit data and may provide answers about what happened to the plane, which was carrying 227 passengers and 12 crew when it vanished on 8 March and flew thousands of kilometres off its Kuala Lumpur-to-Beijing route.
However, the batteries in the beacons have already reached the end of their 30-day expected life, making efforts to swiftly locate them all the more critical.
Authorities say evidence suggests the plane was deliberately diverted by someone familiar with the aircraft, but have not ruled out mechanical problems.
Analysis of satellite data led investigators to conclude the Boeing 777 came down in a remote area of the Indian Ocean, some 2,261kms northwest of the Australian city of Perth.
At the weekend, the sophisticated US Navy TPL picked up what officials said were two signals consistent with black box locator beacons, the first for more than two hours and the second for about 13 minutes.
Today, Mr Houston said that another ping was detected on yesterday afternoon and lasted five minutes, 25 seconds, while a second was picked up last night and lasted seven minutes.
That brings to four the number of pings found in the area.
However, two US Navy officers told Reuters today that while the pings had been found within a 1,300 square kilometre area, they were not confident that they represented recurrences of the same signal.
"I'd say they are separate acoustic events," said US Navy Captain Mark Matthews, citing the fact that the pings are not close together.
"There has been variability in the geographic position, which leads me to be less optimistic than I would be if I could consistently re-acquire the signal so that I have a nice, small geographic area to focus the autonomous under water vehicle search on," he added.
An autonomous underwater vehicle named Bluefin-21 is on board the Ocean Shield and could be sent to look for wreckage on the sea floor once intelligence narrows the search area.
The potential search area is currently about 4.5 km deep, the outer reach of the Bluefin's range.