The head of the U.S. Central Intelligence Agency says al-Qaida in the Arabian Peninsula currently poses the most serious terrorism threat to the United States.

CIA Director David Petraeus spoke at a congressional hearing Tuesday on evaluating U.S. counterterrorism efforts 10 years after the September 11, 2001, terrorist attacks.

Petraeus said while the South Asian core of al-Qaida has been weakened, its affiliates in other areas — particularly in the Arabian Peninsula — have grown stronger and more able to conduct attacks. He noted that al-Qaida in the Arabian Peninsula has made at least two unsuccessful attempts to attack the United States in the past two years.

FBI Director Robert Mueller spoke at a later hearing Tuesday, where he said in addition to al-Qaida in the Arabian Peninsula, “homegrown” violent extremists are among the most serious threats to U.S. security. He said terrorist groups and their online postings inspire and inform would-be terrorists about how to launch an attack.

Homeland Security Secretary Janet Napolitano said that U.S. security operations must be active overseas, where most attacks against the United States have been planned.