The United States has rejected claims that sanctions imposed on Iran last year have hampered rescue efforts in areas where at least 45 people have died in severe flooding in the country.
US Secretary of State Mike Pompeo instead insisted Tehran's "mismanagement" of urban planning and emergency preparedness has led to the ongoing disaster.
Many have died in the past two weeks from flash floods after the heaviest rains to hit the country for at least a decade.
Flooding has affected at least 26 out of Iran's 31 provinces since heavy downpours began on March 19 with tens of thousands of people evacuated from homes in flooded locales.
Iran said Germany and Britain have offered them humanitarian aid, including 40 boats, but said renewed US sanctions had disrupted relief efforts.
President Donald Trump last year restored crippling sanctions and Iranian foreign minister Mohammad Javad Zarif tweeted that America's "maximum pressure" policy on Iran "is impeding aid efforts by #IranianRedCrescent to all communities devastated by unprecedented floods".
"This isn't just economic warfare; it's economic Terrorism," he tweeted.
Pompeo said the US is sympathetic to the victims and is willing to provide assistance for flood relief efforts but only through the International Red Cross and Red Crescent societies.
"The regime blames outside entities when, in fact, it is their mismanagement that has led to this disaster," Pompeo said.
"The United States stands ready to assist and contribute to the International Federation of Red Cross and Red Crescent Societies, which would then direct the money through the Iranian Red Crescent for relief."
Iran has seen a decades-long drought but the latest flooding is also blamed on disregard for safety measures and construction near rivers.
