WASHINGTON, April 29 (Xinhua) -- A senior U.S. intelligence official said the core al-Qaeda group led by Osama bin Laden has been surpassed by its affiliates as the biggest terrorist threat to the United States, American Forces Press Service reported on Sunday, on the eve of the one-year anniversary of bin Laden's death.

"With bin Laden's death, the global jihadist movement lost its most iconic, most effective and most inspirational leader," Robert T. Cardillo, Deputy Director of National Intelligence for intelligence integration, told reporters in a conference call earlier this week.

Bin Laden's death allowed al-Qaeda second-in-command Ayman al Zawahiri to move up, but "he has not changed the group's strategic direction and does not have the charisma to appeal to new recruits," Cardillo said.

He noted that the al-Qaeda offshoots in areas like the Arabian Peninsula and Somalia will surpass the core al-Qaeda remaining in Pakistan, and each group will "seek opportunities to strike western interests" with "different intent and opportunity to execute those plans."

Cardillo also said prolonged instability in Tunisia, Egypt and Yemen would give al-Qaeda, its affiliates and its allies more time to establish networks, gain support and potentially engage in operations.

Wednesday would mark the one-year anniversary of the U.S. killing of bin Laden, which was ordered by U.S. President Barack Obama.