WASHINGTON (AP) — A senior member of the al-Qaida spinoff group behind the failed Christmas Day airline attack was killed as part of a U.S.-Yemeni counterterrorism campaign, the terror group announced.

Nayif al-Qahtani's death was revealed in an al-Qaida Arabian Peninsula newsletter a week after the U.S. slapped terror sanctions on him.

Gregory Johnsen, a terrorism expert at Princeton University who reviewed the Arabic newsletter, said Thursday that al-Qahtani was a pioneering figure who helped turn Yemen's upstart group into a formidable terrorist network.

The group surprised U.S. officials in December when it nearly detonated a bomb aboard a U.S.-bound jetliner. Until then, the group had been regarded as threat primarily in Yemen.

The bomb failed to detonate but revealed persistent gaps in the U.S. intelligence system. A Nigerian man, Umar Farouk Abdulmutallab, was charged with the attempted bombing. U.S. intelligence officials have linked him directly to Yemen's al-Qaida group.

Johnsen said al-Qahtani's death was unlikely to cripple the organization. Since al-Qahtani helped bring the group to prominence, other figures have taken on more leadership roles in the group.

The newsletter did not say when al-Qahtani was killed but said he died in Yemen's southern Abyan province. Yemen's government, working closely with U.S. counterterrorism officials, have carried out several airstrikes against al-Qaida there, including back-to-back days of bombing Sunday and Monday.

Johnsen said al-Qahtani likely has been dead for some time, and he may have been dead already when the U.S. announced the sanctions.