U.S. forces struck Iran's three main nuclear sites, President Donald Trump said late on Saturday, and he warned Tehran it would face more attacks if it did not agree to peace.

After days of deliberation and long before his self-imposed two-week deadline, Trump's decision to join Israel's military campaign against its major rival Iran represents a major escalation of the conflict.

"The strikes were a spectacular military success," Trump said in a televised Oval Office address. "Iran's key nuclear enrichment facilities have been completely and totally obliterated."

In a speech that lasted just over three minutes, Trump said Iran's future held "either peace or tragedy," and that there were many other targets that could be hit by the U.S. military.

"If peace does not come quickly, we will go after those other targets with precision, speed and skill."