The report, to be delivered to the board of the International Atomic Energy Agency later Friday, will include the figure of 27 percent enrichment, the diplomat said, a potentially alarming development since it moves the purity of Iran’s uranium enrichment closer toward bomb-grade material even as world powers are negotiating with Tehran to shift its nuclear program in the opposite direction.

Whether the 27 percent figure represents a trace amount or a substantial quantity appears for the moment to be unknown publicly.

The diplomat, speaking on the condition of anonymity because of the issue’s sensitivity, cautioned that I.A.E.A. is investigating the reading and that the spike in purity could turn out to be accidental.

“There’s a decent chance that it’s an operator error,” the diplomat said.