Iran's Supreme Leader Ali Khamenei said on Friday that Tehran has no proxies in the region and that the groups it backs act independently.
US President Donald Trump said on Monday he would hold Iran responsible for any attacks carried out by Yemen’s Houthi militias that it says Iran supports in Yemen.
"America needs to know that if it messes with Iran, it will receive a severe slap," said Khamenei.
Foreign Minister Abbas Araqchi said on Thursday that Iran will consider the "opportunities" as well as the threats in a letter from Trump that urged it to reach a new nuclear deal, and will soon respond.
Khamenei rejected Trump's letter last week as deceptive, saying Trump's excessive demands would "tighten the knot of sanctions and increase pressure on Iran".
But Araqchi said Tehran was still evaluating the letter and weighing its reply.