US interests around the world will be harmed if America launches an attack against Iran, Supreme Leader Ayatollah Ali Khamenei has said.
Ayatollah Khamenei says Iran will not heed US threats
"The Iranian nation will respond to any blow with double the intensity," he added, in comments reported on TV.
Iran has been reported to the UN Security Council, amid Western fears Iran is seeking atomic weapons.
The UN is seeking a diplomatic solution but the US has not ruled out military strikes against Iranian nuclear sites.
Addressing workers in Tehran on International Labourers' Day, Ayatollah Khamenei said Iran would not heed US "threats and intimidation".
"The Iranian nation and its officials are peace-seekers and the Islamic republic would not invade anybody," he added.
Calls for tough action
The Security Council demanded on 29 March that Iran comply with the demands of the International Atomic Energy Agency (IAEA) for a "full and sustained suspension" of its uranium enrichment work.
The head of the IAEA, Mohammed ElBaradei, is expected to report back to the council at noon on 28 April.
On Wednesday, the head of Iran's nuclear agency met Mr ElBaradei for 11th-hour talks before the Friday meeting.
Vice-President Gholam Reza Aghazadeh, accompanied by deputy Mohammed Saidi and Ali Asghar Soltanieh, Iran's ambassador to the IAEA, made no comment as they entered IAEA headquarters in Vienna.
No details of the meeting have been released as yet.
The US is trying to rally support from the Security Council for tougher action against Iran, including sanctions - a move currently being resisted by Russia and China.
Iran insists its nuclear programme is for civilian energy purposes only.
Iranian President Mahmoud Ahmadinejad said on Wednesday that Iran's "enemies" would not be able to use the Security Council and the IAEA to punish Iran.
"The illegitimate and right-nullifying decision could not get legitimacy under cover of council and the agency," he said, according to a state TV broadcast.