Investigators probing the disappearance of Malaysia Airlines Flight MH370 suspect that the co-pilot of the airliner tried to make a call with his mobile phone after the plane was diverted from its scheduled route.

Malaysia's New Straits Times newspaper yesterday cited unidentified investigative sources as saying the attempted call from co-pilot Fariq Abdul Hamid's phone was picked up by a mobile-phone tower as the plane was about 200 nautical miles northwest of the west coast state of Penang. That was roughly where military radar made its last sighting of the missing jet at 2:15am local time on March 8.

"The telco's (telecommunications company's) tower established the call that he was trying to make. On why the call was cut off, it was likely because the aircraft was fast moving away from the tower and had not come under the coverage of the next one," the New Straits Times cited a source as saying.

The New Straits Times quoted acting transport minister Hishammuddin Hussein as saying that the report needed to be verified. But he appeared to cast doubt on the report by saying: "If this did happen, we would have known about it earlier."

The New Straits Times cited separate investigative sources as saying that a signal had been picked up from Fariq's cellphone, but that it could have been from the device being switched on rather than being used to make a call.

Malaysia is focusing its criminal investigation on the cabin crew and the pilots of the plane - 53-year-old captain Zaharie Ahmad Shah and 27-year old Fariq - after clearing all 227 passengers of any involvement.

Investigators believe that someone with detailed knowledge of both the Boeing 777-200ER and commercial aviation navigation switched off the plane's communications systems before diverting it thousands of miles off its scheduled course.

The search for the missing airliner in the southern Indian Ocean resumed yesterday, amid fears that five weeks after its disappearance batteries powering signals from the black box recorder on board may have died

Australian Prime Minister Tony Abbott warned on Friday that signals picked up during the search in the remote southern Indian Ocean, believed to be "ping" signals from the black box recorders, were fading.

Analysis of satellite data has led investigators to conclude the Boeing 777 crashed into the ocean somewhere west of the Australian city of Perth.

So far, four "pings", which could be from the plane's black box recorders, have been detected in the search area in recent days by a US Navy "Towed Pinger Locator".

"We are now getting to the stage where the signal from what we are very confident is the black box is starting to fade and we are hoping to get as much information as we can before the signal finally expires," Abbott said on Friday.

Batteries in the black box recorder are already past their normal 30-day life, making the search to find it on the murky sea bed all the more urgent. Once they are confident they have located it, searchers then plan to deploy a small unmanned "robot" known as an Autonomous Underwater Vehicle.

"Work continues in an effort to narrow the underwater search area for when the Autonomous Underwater Vehicle is deployed," the Australian agency co-ordinating the search said yesterday.

"There have been no confirmed acoustic detections over the past 24 hours," it said in a statement.