Al-Shabab extremists in Somalia remain “a potent threat” to regional peace and are now manufacturing home-made explosives, expanding their revenue sources and infiltrating government institutions, U.N. experts say.

The panel of experts’ report to the Security Council, circulated Tuesday, said a significant escalation of U.S. airstrikes targeting al-Shabab militants and leaders has kept the al-Qaida-linked group “off-balance” but has had “little effect on its ability to launch regular asymmetric attacks throughout Somalia.”

The report said al-Shabab’s assault on Jan. 15 on a commercial business complex in Nairobi, Kenya, containing the DusitD2 Hotel “illustrates the danger the group continues to pose to regional peace and security.” That attack killed 21 people as well as four gunmen.

Read more: Washington Post