UNITED NATIONS — Al-Qaida's senior leadership has a diminished ability to direct global terror operations but the threat from loosely linked affiliates and individuals radicalized by its "infectious ideas" is becoming more sophisticated, U.N. experts said Wednesday.

In a report to the Security Council, the panel monitoring U.N. sanctions against al-Qaida pointed to the growing sophistication and reach of terrorist propaganda on the Internet. It also pointed to recent attacks in Boston, London and Paris that highlight the "persistent challenge" of terrorist acts committed by individuals or small groups and the emergence of a strong al-Qaida presence in Syria's civil war.

"Individuals and cells associated with al-Qaida and its affiliates continue to innovate with regard to targets, tactics and technology," the report said.

"While the threat posed by al-Qaida as a global terrorist organization has declined, the threat posed by its affiliates and its infectious ideas persists," it said.

The report was written before the Obama administration's decision to close 19 U.S. embassies and consulates in 16 countries in the Middle East and Africa, triggered by an intercepted secret message between al-Qaida chief Ayman al-Zawahri and his deputy in Yemen about plans for a major terror attack.

But the U.N. experts' assessment largely coincides with the Obama administration's stance on al-Qaida.

U.S. State Department spokesman Jen Psaki said Tuesday that despite the recent embassy closures, the administration believes "the leadership of the al-Qaida core has been weakened, decimated."

"But we remain concerned about the threat from affiliates," Psaki said.

The U.N. experts said the waning influence of al-Qaida's leaders is evident in al-Zawahri's unsuccessful attempts to mediate internal conflicts between al-Qaida and Jabhat al-Nusra, an affiliate of al-Qaida in Iraq that has been fighting against the Syrian government. Al-Zawahri, who replaced Osama bin Laden, also was unable to end infighting within Somalia's al-Shabab militants.

"A degraded senior leadership based in the Afghanistan-Pakistan border region continues to issue statements, but demonstrates little ability to direct operations through centralized command and control," the experts said.

Nonetheless, the experts said, "its rhetoric and its calls for attacks continue to mobilize violent radicals, regardless of where they are based."

As a result, they said "al-Qaida affiliates pursue autonomous agendas even as they draw on al-Qaida branding."

The 31-page report by the U.N. experts provides a lengthy discussion of al-Qaida affiliates, saying some have gained traction by taking advantage of local conflicts in countries like Syria and Yemen while others are losing influence because of military operations or political dialogue.

In Mali and Somalia, military operations "have significantly diminished the operating space available to affiliates" while in the Philippines, peace talks have reduced the influence of al-Qaida affiliates, it said.

"However, the diversification of al-Qaida affiliates has not reduced the threat that they pose, to civilians, national governments or selected targets in the international community," the experts said. "These attacks are largely contained within the operating areas of each affiliate."

The experts said al-Qaida affiliates can train recruits, innovate in planning for attacks, and carry out operations.

The Pakistan-based militant group Lashkar-e-Taiba continues to provide advanced terrorist training, including on improvised explosive devices, they said, while Al-Qaida in the Islamic Maghreb has developed significant expertise in kidnapping for ransom.

Al-Qaida in the Arabian Peninsula remains a major source of technological innovation and, along with al-Shabab, continues to support high-quality digital propaganda operations, the experts said.

The experts stressed that al-Qaida's "rhetoric and its calls for attacks continue to mobilize violent radicals, regardless of where they are based."

They called for intensified efforts to implement a U.N. travel ban, especially against those trying to promote networking among al-Qaida affiliates, which can "increase the threat by transferring skills and knowledge as well as creating new networks or strengthening existing ones."