Washington DC - President Donald Trump on Thursday warned Iran to "get serious soon" in talks to end his unprovoked war and once again slammed NATO allies for not joining in the conflict.

Trump insisted Iran was actively talking with the US on a deal to end the nearly four-week war, despite public denials from Iranian officials.

"The Iranian negotiators are very different and 'strange,'" he wrote in early morning post on Truth Social.

"They are 'begging' us to make a deal, which they should be doing since they have been militarily obliterated, with zero chance of a comeback, and yet they publicly state that they are only 'looking at our proposal.' WRONG!!!"

Iran "better get serious soon, before it is too late," he urged, "because once that happens, there is NO TURNING BACK, and it won't be pretty!"

Pakistan has confirmed that it delivered a 15-point US plan to Iranian officials, with Foreign Minister Ishaq Dar on Thursday saying that "indirect talks" were taking place with Islamabad as intermediary.

Trump on Thursday also took aim again at NATO allies, after describing them last week as "cowards" for not joining the US and Israel in their aggression against Iran.

"NATO NATIONS HAVE DONE ABSOLUTELY NOTHING TO HELP WITH THE LUNATIC NATION, NOW MILITARILY DECIMATED, OF IRAN," he wrote in a separate Truth Social post, while also once again casting doubt on US support for the alliance going forward.

"THE U.S.A. NEEDS NOTHING FROM NATO, BUT 'NEVER FORGET' THIS VERY IMPORTANT POINT IN TIME!"