"The Soviet Union collapsed without a revolution. A transformation is possible. But in Iran, I fear change will be violent, and the current regime will not go quietly," Issa said.

US President Donald Trump mooted regime change and even killing Iran's Supreme Leader Ali Khamenei at the height of combat amid a 12-day war between Iran and Israel last month.

As a ceasefire took hold, the administration backed away from the hawkish rhetoric but a senior Trump aide said this week that change could only come from within.