In a post on Truth Social, Trump, who has said Iran can call if it wants to talk and has stressed repeatedly Tehran cannot have a nuclear weapon, said the country "couldn't get its act together".
The Wall Street Journal cited US officials as saying the president had instructed aides to prepare for an extended blockade of Iran's ports in a bid to force Tehran to capitulate.
Officials said Trump had opted to continue squeezing Iran's economy and oil exports with the blockade as his other options - resuming bombing or walking away from the conflict - carried more risk, according to the WSJ.
"They don't know how to sign a non-nuclear deal. They'd better get smart soon!" Trump said in the post on Wednesday, without explaining what such a deal would entail.
Iran wants some kind of US acknowledgment of its right to enrich uranium for what it says are peaceful, civilian purposes.
It has a stockpile of roughly 440 kilograms of uranium enriched to 60 per cent, material that could be used for several nuclear weapons if further enriched.
Iranian officials said on Tuesday the country could withstand the blockade as it was using alternative trade routes, and the Islamic Republic did not consider the war over.
The conflict has killed thousands, thrown energy markets into turmoil and disrupted global trade routes.
Iran's most recent offer for resolving the two-month war, suspended since April 8 under a ceasefire agreement, would set aside discussion of its nuclear program until the conflict is formally ended and shipping issues resolved.
That proposal did not meet Trump's demand to have the nuclear issue discussed from the outset, however.
Tehran has largely blocked all shipping apart from its own from the Gulf through the Strait of Hormuz, a choke point for global energy supplies, since the war began on February 28.
In April, the US began blockading Iranian ships.
Trump's Truth Social post featured a mock-up image of himself in dark glasses and wielding a machine gun with the caption "No more Mr Nice Guy".
Hopes of a swift resolution to the conflict have receded since Trump last weekend scrapped a visit by his special envoy Steve Witkoff and son-in-law Jared Kushner to mediator Pakistan.
Iranian Foreign Minister Abbas Araqchi visited the country twice on the weekend of April 25-26.
Since several senior Iranian political and military figures were killed in US-Israeli strikes, Iran no longer has a single, undisputed clerical arbiter at the pinnacle of power, which may be hardening Tehran's negotiating stance.
The killing of Ayatollah Ali Khamenei on the first day of the war, and the elevation of his wounded son, Mojtaba, to replace him as supreme leader, has handed more power to hardline commanders of the Islamic Revolutionary Guard Corps, Iranian officials and analysts say.
Trump is under domestic pressure to end a war for which he has given the US public shifting rationales.
His approval rating fell to the lowest level of his current term, as Americans increasingly soured on his handling of the cost of living and the unpopular war, according to a Reuters/Ipsos poll.
Oil prices rose nearly three per cent on Wednesday, with the Brent contract hitting a one-month high, on concerns that an extended blockade of Iranian ports would prolong supply disruptions.
