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U.S. officials rebuked Boeing for comments its executives made at a media briefing on plans to get the grounded 787 Dreamliner flying again.

The National Transportation Safety Board (NTSB) said Boeing didn’t inform investigators what it planned to say in the March 15 briefing in Tokyo, which is “inconsistent with our expectations” from a company involved in an accident probe, agency General Counsel David Tochen wrote in a letter Thursday.

The letter signals tension in an investigation with high stakes for Boeing, which is trying to limit damage to the image of its high-efficiency plane once it’s cleared to resume flights.

The NTSB stopped short of restricting Boeing’s access to its investigation, one of two into 787 batteries that overheated and emitted fumes.

Though the NTSB didn’t say in the letter which comments in the Boeing briefing it found objectionable, there were at least three instances where Boeing executives’ comments in that briefing clashed with the public positions of the NTSB.

Mike Sinnett, vice president and chief project engineer for the 787, appeared to challenge the NTSB’s use of the term “thermal runaway.”

The safety agency defines that as an uncontrolled chemical reaction occurring at high temperatures inside the battery, and it says that happened during a Jan. 7 fire in Boston involving the lithium-ion battery on a Japan Airlines 787.

Sinnett insisted in Tokyo that under Boeing’s definition of the term, there had been no thermal runaway.

He also said that the NTSB’s preliminary findings indicated there hadn’t been flames within the battery case. When asked about that the next day, NTSB spokesman Peter Knudson said investigators hadn’t ruled out fire within the battery case.

More broadly, Sinnett’s remarks painted a very different picture of the seriousness of the two 787 battery incidents in which a battery overheated and emitted fumes — than described by NTSB chair Deborah Hersman.

“We do not expect to see fire events on board aircraft,” Hersman said in January. “One of these events alone is serious; two of them in close proximity, especially in an airplane model with only about 100,000 flight hours, underscores the importance of getting to the root cause of these incidents.”

In contrast, Sinnett played down the risks. “We can say with certainty that after the battery failed, the airplane responded exactly as we had designed and intended,” Sinnett said. “What we saw when the battery failed was damage that was limited to the function of the battery and the immediate area of the battery, but the airplane was not at risk.”

The Federal Aviation Administration grounded the 787 on Jan. 16.

Boeing officials at the briefing said their proposed design changes to the Dreamliner’s battery systems may allow commercial flights to restart within weeks.

Information from Seattle Times aerospace reporter Dominic Gates is included in this report.