Officials at the National Transportation Safety Board (NTSB) in the United States have warned the results of a probe into battery problems on the Boeing Dreamliner may still be “weeks” away.

All of the aircraft currently in service are presently grounded following a series of incidents in January.

A battery on one Dreamliner caught fire, while a malfunction forced another to make an emergency landing last month.

“I would not want to categorically say that these batteries are not safe,” said Deborah Hersman, head of the NTSB.

“Any new technology, any new design, there are going to be some inherent risks.

“The important thing is to mitigate them.”

Hersman added the NTSB was “running through the macro level to the microscopic level on this battery”.

“But I think we are probably weeks away from being able to tell people here’s what exactly happened and what needs to change.”

There are presently 50 Dreamliners in use around the world.

However, Boeing has already cancelled deliveries of the aircraft.

It has orders for 800 Dreamliners and a long delay in approval to fly again is likely to delay delivery schedules further.

In a statement Boeing welcomed the news: “Boeing welcomes the progress reported by the US National Transportation Safety Board in the 787 investigation, including that the NTSB has identified the origin of the event as having been within the battery.

“The findings discussed today demonstrated a narrowing of the focus of the investigation to short circuiting observed in the battery, while providing the public with a better understanding of the nature of the investigation.

The statement added: “The company remains committed to working with the NTSB, the US Federal Aviation Administration and our customers to maintain the high level of safety the traveling public expects and that the air transport system has delivered.

“We continue to provide support to the investigative groups as they work to further understand these events and as we work to prevent such incidents in the future.

“The safety of passengers and crew members who fly aboard Boeing airplanes is our highest priority.”