Iran could reduce its co-operation with the UN nuclear watchdog, President Hassan Rouhani told the body's head on Wednesday, reports Reuters.
He warned US President Donald Trump of "consequences" of fresh sanctions against Iranian oil sales.
In May, Trump pulled out of a multinational deal under which sanctions on Iran were lifted in return for curbs to its nuclear programme, verified by the International Atomic Energy Agency (IAEA).
Washington has since told countries they must stop buying Iranian oil from Nov 4 or face financial measures.
"Iran's nuclear activities have always been for peaceful purposes, but it is Iran that would decide on its level of cooperation with the IAEA," Iranian state news agency IRNA quoted Rouhani as saying after meeting IAEA head Yukiya Amano in Vienna.
"The responsibility for the change of Iran's cooperation level with the IAEA falls on those who have created this new situation," he added.
Rouhani said earlier in the day Tehran would stand firm against US threats to cut Iranian oil sales.
"The Americans say they want to reduce Iranian oil exports to zero ... It shows they have not thought about its consequences," Rouhani was quoted as saying by IRNA.
On Tuesday, Rouhani hinted at a threat to disrupt oil shipments from neighbouring countries if Washington tries to cut its exports.