WASHINGTON -- Four US troops have been killed in action and 18 others seriously wounded during the ongoing military operation against Iran as of Monday morning, according to US Central Command spokesperson Tim Hawkins.

The identities of the fallen are being withheld until 24 hours after next of kin notification, the command said in a statement.

All four died in the same attack in Kuwait, CNN reported.

Earlier on Monday, US President Donald Trump told New York Post that he is not ruling out sending US ground troops into Iran if necessary. Trump later suggested that the campaign could last beyond four to five weeks.

US Chairman of the Joint Chiefs of Staff Dan Caine said Monday at a Pentagon briefing that the US attack on Iran is in its early stages and more US troops and fighter jets are arriving in the Middle East.

"We expect to take additional losses," Caine acknowledged.