The mobile phone of Fariq Abdul Hamid, the 27-year-old co-pilot of Malaysia Airlines Flight MH370, was on and made contact with a cell tower in Penang.

A U.S official told CNN that the signal was detected about 400 kilometres from where the flight transponder last sent a signal, and the phone was searching for service roughly 30 minutes after the plane made a sharp turn westward.

This followed reports by the New Straits Times (NST) that the first officer tried to make a call while the plane was in flight.

"As far as I know, no, but as I said that would be in the realm of the police and the other international (authorities) and when the time comes that will be revealed. But I do not want to speculate on that at the moment," said Acting Transport Minister Datuk Seri Hishammuddin Tun Hussein.

However, the U.S official familiar with the investigation of the missing plane said that no other mobile phone signals were picked up by the Penang tower.

Meanwhile, efforts to find the aircraft beneath the choppy surface of the southern Indian Ocean have been intensified with a U.S Navy-contracted submersible diving towards the sea floor.

However, just six hours of searching for underwater debris, Bluefin-21 returned to the surface due to a built-in safety feature, according to the Joint Agency Coordination Centre in Perth, Australia.

It is however unclear how much of the 5 kilometer by 8 kilometer search area the Bluefin scanned and it might take up to two months to scan the entire search area, said the report.

Another possible lead in the plane’s disappearance was the detection of an oil slick by the Australian ship Ocean Shield on Sunday evening.

A two-liter sample had been collected for examination but will take a few days to analyze.

A total of 12 aircraft and 15 ships were involved in Monday’s search effort on the surface, covering a 47,600-square-kilometer area, might be among the last said Houston.

"The air and surface search for floating material will be completed in the next two to three days in the area where the aircraft most likely entered the water," Houston said.

The search was hyped up last week when Navy-owned pinger locator and sonobuoys detected sounds that could have been from the plane’s black boxes, or data and voice recorders.

However, after weeks of silence, the likely hood of the batteries powering the beacons are dead is high, with the 30 day deadline passed.