"We hope that they do not make a new strategic mistake and certainly in the case of any strategic mistake, they will witness Iran's decisive response," government spokesman Ali Rabiei told a televised news conference on Tuesday.
A US media report, quoting unnamed officials, said that an alleged Iranian scheme to kill the US ambassador to South Africa was planned before the US presidential election in November.
"Any attack by Iran, in any form, against the United States will be met with an attack on Iran that will be 1,000 times greater in magnitude!" Trump wrote on Twitter on Monday.
Rabiei expressed regret that "the president of a country who has claims to global management and order would make hasty, agenda-fueled and dubious remarks on such a weak basis."
He warned that reacting to such reports would "achieve nothing but disruption to the region and to world calm" and advised Trump to "refrain from fresh adventurism... for the sake of winning a new term as president."
On Monday, the Foreign Ministry denied the report of an assassination plot as "baseless" and part of "repetitive and rotten methods to create an anti-Iranian atmosphere".
"The Islamic Republic of Iran, as a responsible member of the international community, has demonstrated its continued adherence to the principles and customs of international diplomacy,” the Foreign Ministry said in a statement.
It noted that “news fabrications” is part of “the Trump administration counter-intelligence campaign against Iran and that such moves will continue in the run-up to the US presidential election but will certainly remain “futile”.
A spokesman for South Africa’s Foreign Ministry said the US officials’ allegation took Pretoria by surprise.
Relations between Washington and Tehran have been tense ever since the Islamic Revolution of 1979. They have deteriorated sharply since Trump unilaterally pulled out of a landmark international nuclear deal with Iran in May 2018 and reimposed tough sanctions.
The Iranian Navy said last week that it drove off US aircraft that flew close to an area where naval exercises were underway near the sensitive Strait of Hormuz.
The military said three US aircraft were detected by air defenses.
One of them was a US RQ-4 drone, the same model as one shot down by Iran in June last year after violating Iranian airspace.
On January 3, the United States assassinated Lieutenant General Soleimani along with Abu Mahdi al-Muhandis, the second-in-command of Iraq’s Popular Mobilization Units and several other companions, outside Baghdad airport.
Iran responded by firing a volley of ballistic missiles at US forces based in Iraq, which left about 110 American troops injured.
AFP and Press TV contributed to this story.