Israel and the United States have launched strikes on Iran on Saturday morning with explosions being reported in multiple Iranian cities including capital Tehran.

US President Donald Trump described the military campaign as “massive and ongoing,” and intended to prevent the country from putting US lives at risk. He said Iran had been working to rebuild its nuclear program after a June US bombing run on its nuclear facilities, said a CNN report.

Israel declared a state of emergency across the country as the strikes were launched, in anticipation of Iranian retaliation. 

An Iran official said the country is preparing for retaliation. The official said the response is set to be crushing.

In  a message on his social media account, Trump said:

"A short time ago the U.S. military began major combat operations in Iran. Our objective is to defend the American people by eliminating imminent threats from the Iranian regime. Iran can never have a nuclear weapon."

"We sought repeatedly to make a deal. Iran attempted to rebuild their nuclear programme. Iran is developing long range missiles that threaten the US and others."

"We are going to destroy their missiles and raze their missile industry to the ground. We’re going to annihilate their navy."

"We will ensure that Iran does not obtain a nuclear weapon."

President Donald Trump said in his video that American lives may be lost as a result of his military operation inside Iran.

“The Iranian regime seeks to kill. The lives of courageous American heroes may be lost and we may have casualties — that often happens in war — but we’re doing this not for now. We’re doing this for the future, and it is a noble mission,” the president said.

He he said the US had “taken every possible step to minimize the risk to US personnel in the region.”

“We have a big decision to make,” he told a crowd in Corpus Christi, Texas, where he was promoting his energy agenda, said a CNN report.

“They want to make a deal, but got to make a deal that’s meaningful,” the president said. “I’d rather do it the peaceful way. But they’re very difficult people.”

Trump has increased diplomatic and military pressure on Iran in the weeks since an Iranian crackdown on protesters, attempting to force the country's rulers to forswear nuclear weapons and other activities Washington sees as destabilising.