WASHINGTON -- US President Donald Trump said Monday that he is not ruling out sending US ground troops into Iran if necessary.

"I don't have the yips with respect to boots on the ground — like every president says, 'There will be no boots on the ground,' I don't say it," Trump told New York Post in an interview.

"I say 'probably don't need them,' (or) 'if they were necessary,'" he said.

Trump claimed that the military campaign launched on Saturday morning was "way ahead of schedule" in terms of killing dozens of senior Iranian officials.

On Sunday, Trump told The New York Times that he estimated the war would last four to five weeks.

A Reuters/Ipsos poll conducted Saturday and Sunday found that some 43 percent of US citizens disapproved of the strikes and just 27 percent approved. Another 29 percent said they were not sure.

"I think that the polling is very good, but I don't care about polling," Trump said in the interview.

On Monday, Secretary of Iran's Supreme National Security Council Ali Larijani said the country is prepared for a long war.

"Iran, unlike the United States, has prepared itself for a long war," Larijani said in a post on social media platform X.

"As in the past 300 years, Iran did not start this war, and our brave Armed Forces have not engaged in any attacks except in defense. We will fiercely defend ourselves and our six thousand years old civilization regardless of the costs and will make the enemies sorry for their miscalculation," he said.