Donald Trump sharply rejected Iran's latest response to a U.S.-backed peace proposal on Sunday, escalating tensions around fragile ceasefire negotiations and raising new questions about whether diplomacy between Washington and Tehran can survive.

The president reacted after Iranian media reported that Tehran had delivered its response through Pakistani mediators following more than a week of waiting by the White House.

"I have just read the response from Iran's so-called 'Representatives.' I don't like it - TOTALLY UNACCEPTABLE! Thank you for your attention to this matter. President DONALD J. TRUMP," Trump wrote on Truth Social.

In a brief phone interview with Axios later Sunday, Trump doubled down on his criticism but declined to explain specifically what in the Iranian proposal had triggered his reaction.

"I don't like their letter. It's inappropriate. I don't like their response," Trump said. "They have been tapping along many nations for 47 years."

The remarks represented the first direct response from the Trump administration since Iran reportedly submitted its counterproposal aimed at ending the conflict that erupted earlier this year after U.S. and Israeli military strikes on Iranian nuclear-linked sites.

Analysts following the negotiations said Trump's comments appeared to reject several of Iran's key demands simultaneously, including efforts to ease sanctions, end the U.S. naval blockade and preserve parts of Tehran's uranium enrichment programme.

The president also intensified his rhetoric surrounding Iran's enriched uranium stockpile during an interview aired Sunday on "Full Measure," warning that the U.S. military was closely monitoring the material believed to remain buried beneath damaged nuclear facilities.

"We'll get that at some point, whenever we want. We have it surveilled," Trump said.

"If anybody got near the place, we will know about it, and we'll blow them up."

The uranium dispute has become central to negotiations between Washington and Tehran. The U.S. has insisted Iran dismantle its enrichment programme entirely, while Iranian officials argue that surrendering nuclear capabilities would cross a political red line.