Iran has said it will not suspend uranium enrichment, a key demand of an international proposal aimed at resolving the nuclear programme row.
Iran has launched a series of wargames to test its military
It comes two days before Iran was due to respond to a proposal by Russia, China, France, Britain, Germany and the US aimed at resolving the nuclear row.
Iran's foreign ministry said a final decision would be based on negotiations.
But he warned that a halt to uranium enrichment was "not on the agenda".
Enrichment halt 'illogical'
Foreign ministry spokesman Hamid Reza Asefi said suspending enrichment - a key step in the nuclear fuel making process - would be a return to the past.
His comments come a few days after Iran's foreign minister, Manouchehr Mottaki, said the country was ready to discuss the issue, but would explain in any talks that a halt to enrichment would be "illogical".
The international proposal to Iran calls for a suspension of uranium enrichment in return for the partial lifting of economic sanctions and assistance with nuclear technology.
Mr Asefi said Iran's response - expected by Tuesday - would be "multi-faceted", though he did not elaborate.
Iran says its nuclear programme is entirely peaceful
In July, the United Nations Security Council passed a resolution calling on Iran to suspend enrichment by 31 August or face unspecified economic and diplomatic sanctions.
Iran has said that it would respond to any possible sanctions with a painful response - which may involve a cut in its oil production.
On Saturday, Iran launched a series of major military exercises, with 10 short-range surface-to-surface missiles being launched in a test on Sunday.
According to Iranian state television, the tests included a launch of a Saegheh (Lightning) missile, which reportedly has a range of 80 to 250 kilometres (50 to 155 miles).
The missile is not thought to be capable of carrying a nuclear warhead, news agency AP reported.
The Iranian military has said its wargames are a reaction to what it sees as a heightening of tension in the Middle East.
A military training plane caught fire and crashed after trying to make an emergency landing on a highway outside of Tehran. The pilot managed to eject safely.