The recording was undated and the transcript did not clearly point towards a time frame for when it could have been made.

Zawahiri was killed in a U.S. strike in Afghanistan, the biggest blow to the militant group since its founder Osama bin Laden was killed in 2011.

Zawahiri had been in hiding for years, and the operation to locate and kill him was the result of “careful, patient and persistent” work by the counterterrorism and intelligence community, a senior U.S. administration official said.

Al Qaeda has not named a successor. But Saif al-Adel, a mysterious, low-key former Egyptian special forces officer who is a high-ranking member of Al Qaeda, is seen by experts as the top contender.

The United States is offering a reward of up to $10 million for information leading to his arrest.