NEW YORK (AFP) - Boeing chief executive Jim McNerney said Wednesday "good progress" was being made in the international investigation of battery incidents that have all 787 Dreamliners grounded worldwide.

"We do believe good progress is being made in narrowing the cause of these events," McNerney said in an earnings conference call with analysts.

McNerney reiterated that Boeing was "deeply sorry" about the impact on airlines after battery incidents caused aviation regulators around the world to take all 50 787s flying out of service in mid-January.

"Our first order of business for 2013 is to resolve the battery issue on the 787 and return the airplanes safely to service with our customers," McNerney said in an earnings statement.

Last week the US National Transportation Safety Board said investigators were working "around the clock" to understand what sparked the January 7 fire aboard a parked Japan Airlines 787, as well as a smoking battery that forced the emergency landing of an All Nippon Airways 787 on January 16.

Both of the airlines said Wednesday they had been forced to replace a number of batteries in their Dreamliners last year after experiencing problems, well before fire and smoke incidents.

A spokeswoman for All Nippon Airways said 10 batteries on its fleet had been switched, while a JAL representative told AFP "quite a few" had needed changing.

Boeing has halted deliveries of the aircraft as the investigation proceeds, though production continues at a five-unit a month pace.