The commander of U.S. military operations in Africa says he is very worried that three well-known terrorist groups could link up to threaten the United States.

General Carter Ham told reporters in Washington Wednesday that the African-based groups have explicitly and publicly said they intend to target Westerners, specifically Americans.

He said the three groups that pose the biggest threat are Algeria-based Al-Qaida in the Islamic Maghreb, al Shabab, which controls much of Somalia, and Boko Haram, Islamic militants who have claimed responsibility for deadly bombings in Nigeria.

General Ham said all three have talked about plans to closely collaborate and share training and operations.

The general declined to discuss specific counterterrorism steps the United States is undertaking in Africa. Ham said he likes the fact that extremist leaders do not know where the U.S. is, what it is doing, and what it might do.