Investors sent Boeing Co's stock higher on Friday as regulators appeared poised to end a three-month grounding of the high-tech airliner that cost millions of dollars and hurt the reputation of the world's largest planemaker.

Against a weaker U.S. stock market, Boeing shares rose nearly 2.3 percent to $88.06 in early New York trading as the Federal Aviation Administration put finishing touches to a decision watched by airlines and aerospace firms worldwide.

In mid-morning trading, the shares were at $86.77, up 0.75 percent.

The FAA and Boeing declined to comment.

Reuters first reported on Wednesday that the decision to end the flight ban could come within days.

On Friday, two sources close to the matter said the FAA approval could come as early as the afternoon New York time. One noted that there was a good chance an announcement could come Friday but the second said no final decision had been made.

"The go-ahead is imminent but the timing still has to be finalized," said another source familiar with the matter, asking not to be named.

"It could happen today or early next week," a separate source said.

The FAA and other global authorities are reviewing a redesigned battery system aimed at preventing the 787's lithium-ion batteries from catching fire and protecting passengers if they overheat.

The decision to approve the redesigned battery is considered politically sensitive, as investigators have still not found the cause of two battery melt downs on Japanese-owned 787s that prompted regulators to ground the plane in January.

FAA approval would trigger a series of logistical steps by airlines, Boeing mechanics and others in the industry necessary to resume passenger service on the new plane. Other global regulators also must approve Boeing's new design, but were expected to act quickly once the FAA gives its blessing.

In Tokyo on Friday, Japan's Transport Minister said the 787 review was very near completion, but said it was unclear how quickly the plane could resume passenger service.

Boeing has been conducting regular flights with the 787 to test them before delivery, a process that would speed the process of getting 787s to customers who have been waiting throughout the three-month grounding.

"The battery fix review is at the final stage, but I cannot comment now on when the flight resumption will be," Transport Minister Akihiro Ota told reporters.

The grounding has cost Boeing an estimated $600 million, halted deliveries and forced some airlines to lease alternative aircraft. Several airlines have said they will seek compensation from Boeing, potentially adding to the plane maker's losses.

Approval would mean that the FAA believes Boeing's fix is adequate to address the risk of fire on the plane. However, the National Transportation Safety Board continues to investigate what caused a battery to catch fire on a Japan Airlines plane that was parked at the airport in Boston.

The NTSB, the top U.S. transportation investigator, is holding an investigative hearing next week to help it get to the bottom of what caused the fire.

Boeing has said its redesign addresses more than 80 potential causes of fire, and therefore is more rigorous than if a single cause had been found.

(Reporting by Alwyn Scott, Tim Hepher and Andrea Shalal-Esa; Editing by Philip Barbara)