The offer from the United States, France, Britain, China, Russia and Germany came in a letter from European Union foreign policy chief Catherine Ashton, who was responding to an overture last month from Iran, CNN reported.
The six countries made the offer as Iran indicated it would allow international inspectors to visit a key military base in Parchin, southeast of Tehran.
The head of the International Atomic Energy Agency, the U.N. nuclear watchdog, had said Monday inspectors wanted to get to Parchin quickly because of evidence of ongoing activities at the base. International inspectors suspect the base could be involved in a nuclear weapons program.
Iran says its nuclear program is for peaceful purposes only. But Israel, along with the United States and other Western countries, suspect the Islamic Republic is attempting to build a nuclear weapon.
U.S. President Barack Obama Tuesday cited "unprecedented pressure" on Iran from world leaders and said the country is facing a "huge toll" from sanctions and isolation and understands "the world community means business."
Speaking at a Washington news conference, Obama said a diplomatic response to Iran's nuclear program "is deeply in everybody's interests -- the United States, Israel and the world's -- to see if this can be resolved in a peaceful fashion."
Obama's comments came a day after Israeli Prime Minister Binyamin Netanyahu expressed impatience with waiting for results of diplomacy and sanctions on Iran designed to prevent it from developing nuclear weapons.
"Israel must reserve the right to defend itself, and after all, that's the very purpose of the Jewish state: to restore to the Jewish people control over our destiny," said Netanyahu, who was in Washington.
As prime minister of Israel, he said, "I will never let my people live in the shadow of annihilation."