The Iranian foreign ministry's statement came as mediators stepped up efforts to reopen the Strait of Hormuz, which handled 20 per cent of world oil supplies before the war began six months ago and whose status remains the biggest obstacle to a peace deal.
US President Donald Trump's administration on Monday warned countries to cut their business ties with Iran or face secondary sanctions although the Treasury Department stopped short of actually imposing penalties.
Trump reiterated on Thursday that the US was not talking with Iran, while the White House said the US economic campaign would continue until Iran decided to "come to the table in a meaningful way".
Iran's foreign ministry said in a statement all countries were obligated under international law to refrain from implementing US sanctions against Iran, adding that participation in them amounted to complicity in imposing one state's unlawful will on independent states.
It branded the new US measures a "crime against humanity" that put the health and livelihood of millions of civilians at serious risk, and called on other countries and United Nations bodies to uphold the rule of law.
Meanwhile, fears of supply shortages led to long queues at petrol stations in Tehran on Friday.
Motorists were waiting at the petrol pumps in the middle of the night, residents said.
The queues were reportedly in some cases more than 1km long.
At a cabinet meeting this week, President Masoud Pezeshkian acknowledged problems resulting from the war.
Pezeshkian called on the Iranian government itself to exercise restraint with its fleet of vehicles, the ILNA news agency reported.
The public, too, must co-operate, he said.
On Monday, more petrol was sold in Tehran than at any other time this year, the Khabaronline portal reported, citing authorities.
Supreme Leader Ayatollah Mojtaba Khamenei, who was injured and has not been seen publicly since the February 28 attack that killed his father, said in a written statement on Friday that he had banned officials from "committing anything that harms social cohesion".
He urged authorities to avoid any "discouraging statements that weaken national and public motivation," amid concern among Iran's leaders that more financial pressure on its war-battered economy could trigger protests.
Khamenei urged the government to seriously address economic and livelihood challenges including inflation, unemployment, prices and the management of markets for goods and services.
A US official told Reuters on Friday the administration plans to impose limits on Egypt's Banque Misr for doing business with Iran by revoking US financial access to its branches in the United Arab Emirates.
Treasury officials separately issued sanctions targeting one entity based in Hong Kong and one person linked to Iran's Bank Melli, according to a notice posted on the department's website.
With the US focused on its economic pressure campaign, others have sought to revive diplomatic efforts to end the war.
Qatari Prime Minister Sheikh Mohammed bin Abdulrahman al-Thani said he had stressed during talks with Iranian leaders in Tehran on Thursday the importance of returning to the pre-war status of open shipping through the Strait of Hormuz.
Iranian Foreign Minister Abbas Araqchi on Friday described the talks with al-Thani as "creative" and he renewed his appeal to the US to stop putting military and economic pressure on his country and to resume negotiations.
"Putting diplomacy back on track isn't impossible. It hinges on US understanding of one simple fact: pressure doesn't work," Araqchi said on X.
Qatar, a US ally, and Pakistan helped broker a memorandum of understanding in June that led to a ceasefire but that quickly unravelled due to disagreements between Iran and the US over the Strait of Hormuz.
with DPA
