ERBIL, Kurdistan Region of Iraq – US Secretary of Defense Pete Hegseth on Monday urged the Iranian people to take advantage of the opportunity and enact change, after the US and Israel killed Supreme Leader Ayatollah Ali Khamenei in a joint operation against Iran.

"We hope the Iranian people take advantage of this incredible opportunity. President [Donald] Trump has been clear, now is your time," Hegseth told a press briefing on the operational updates of the campaign against Iran.

"To Iranian security forces, choose wisely, President Trump has also been clear about your fate, in either direction," Hegseth warned. 

Trump on Sunday urged the Iranian people to "take back your country" and called on security forces to lay down their arms in exchange for immunity during a video address discussing the progress of combat operations against Iran.

The secretary's remarks come after the US and Israel announced a large-scale military offensive across Iran on Saturday morning. The strikes have killed Khamenei, in addition to several other top Iranian officials. The offensive came following months of escalating tensions between the two sides. 

Hegseth dubbed Operation Epic Fury, Washington's codename for the campaign against Iran, as "the most complex aerial military operation in history," slamming the Islamic republic for pursuing an "expansionist" policy. 

"Iran was building powerful missiles and drones to create a conventional shield for their nuclear blackmail ambitions," Hegseth asserted. "Iran had a conventional gun to our head, as they tried to lie their way to a nuclear bomb." 

"This operation is a clear, devastating, decisive mission: Destroy the missile threat, destroy the navy, and no nukes," Hegseth added.

Hegseth was joined for the briefing by General Dan Caine, chairman of the US Joint Chiefs of Staff, who revealed that the US had achieved "local air superiority" over Iran.

"The flow of forces continues today, in fact, Admiral [Brad] Cooper will receive additional forces even today," the general further noted, referring to the US Central Command (CENTCOM) commander.

The escalations have seen Iran strike back at US bases and interests across the region, with several Middle Eastern countries caught in the midst of fire, including US military installations in Iraq, the Kurdistan Region, Qatar, Saudi Arabia, the UAE, Bahrain, and Kuwait. 

The US has lost at least four service members in the two days of active combat operations against the Islamic republic, the American army's CENTCOM announced Monday. 

Iran’s security chief Ali Larijani said Sunday that the United States and Israel have “set the heart of the Iranian nation ablaze,” after Khamenei was killed, vowing that Tehran will strike its enemies “with a force never seen before.”