"The death of Awlaki is a major blow to al-Qaida's most active operational affiliate," Obama said during a ceremony at Joint Base Myer Henderson Hall in Virginia.
A Yemeni security official said Awlaki, a leader of al-Qaida in the Arabian Peninsula, was killed in an airstrike while traveling between Marib and al-Jawf provinces, areas known to have an al-Qaida presence, The New York Times said. A Defense Ministry statement said several of Awlaki's bodyguards also died.
As a leader of the Arabian Peninsula organization, "he took the lead in planning and directing efforts to murder innocent Americans. … And he repeatedly called on individuals in the United States and around the globe to kill innocent men, women and children to advance a murderous agenda," Obama said.
The president said Awlaki's death marked "another significant milestone" in the effort to defeat al-Qaida and its affiliates.
"Furthermore, the success is a tribute to our intelligence community and to the efforts of Yemen and its security forces, who have worked closely with the United States over the course of several years," he said.
Awlaki's "hateful ideology and targeting of innocent civilians" has been rejected by the vast majority of Muslims and people of all faiths, Obama said.
The action is "further proof that al-Qaida and its affiliates will find no safe haven anywhere in the world," he said.
"Working with Yemen and our other allies and partners, we will be determined, we will be deliberate, we will be relentless, we will be resolute in our commitment to destroy terrorist networks that aim to kill Americans, and to build a world in which people everywhere can live in greater peace, prosperity and security," Obama said.
Tribal officials told The Yemen Observer it wasn't clear whether the airstrike was carried out by the Yemeni air force or a U.S. unmanned aircraft.
U.S. officials say Awlaki helped recruit Nigerian Umar Farouk Abdulmutallab, who was charged with trying to blow up a Northwest Airlines transatlantic flight as it approached Detroit on Christmas Day in 2009.
Officials also said the cleric exchanged e-mails with Army Maj. Nidal Hassan, charged in the 2009 shooting deaths of 12 military personnel and a civilian at Fort Hood in Texas.