Several loud blasts were heard in the Dubai area and over the Qatari capital, Doha, for a second day on Sunday, witnesses said, after Iran launched retaliatory strikes on the neighboring Gulf states in response to U.S. and Israeli strikes on the Islamic Republic.

Iran has said it would target U.S. bases in the region. It has hit a range of other targets.

Iran's paramilitary Revolutionary Guard threatened Sunday to launch its "most-intense offensive operation" ever after the killing of Supreme Leader Ayatollah Ali Khamenei.

"The most-intense offensive operation in the history of the armed forces of the Islamic Republic of Iran will begin in moments, targeting (Israel) and American terrorist bases," it said.

Reuters and The Associated Press contributed to this report.