Iran's chief negotiator Mohammad Bagher Ghalibaf said the United States was seeking to restart the war and hoping Tehran would surrender.
"The enemy's movements, both overt and clandestine, show that despite economic and political pressure, it has not abandoned its military objectives and is seeking to start a new war," Ghalibaf said in an audio message on his official website on Wednesday.
Ghalibaf's remarks came as Tehran and Washington escalated threats while swapping proposals to end the war, which broke out on February 28. A ceasefire has been in place since April 8.
On Wednesday, Iran's Revolutionary Guard warned that the war would expand beyond the region if the US and Israel resume attacks after President Donald Trump said he would strike again unless Tehran agreed to a peace deal.
Ghalibaf said the US was still hoping Iran would surrender and respond favourably to Washington's "excessive demands", by maintaining economic pressure and a naval blockade in place since April 13.
"We must strengthen our preparations for an effective and forceful response to any potential attacks," he said, adding that "Iran will never give in to intimidation, under any circumstances".
Ghalibaf acknowledged the economic pressure on Iranians, while appealing for "national unity".
"Today it is clearer than ever that we are engaged in a war of wills. Whoever wins this war will write Iran's history and determine its future," he said.
