Iran's Fars news agency reported earlier in the day that Tehran's written response to the five permanent UN Security Council members and Germany had been handed to EU officials.
"We have received the letter, but we do not know its contents yet," a diplomatic source said on condition of anonymity.
The letter has first to be analyzed by Solana and negotiators from the so-called Iran Six - China, France, Russia, the United States, the U.K. and Germany.
Iran's top nuclear negotiator and the European Union's foreign policy chief discussed Iran's nuclear program by telephone Monday.
A senior Iranian Foreign Ministry official said prior to the conversation that Tehran would not yield to international demands and back down on its right for civilian nuclear technology.
Iran had failed to give a response by Saturday - an informal deadline set by the six countries involved in the talks - to the proposals designed to persuade Tehran to suspend its uranium enrichment, a process that can be used in nuclear weapons production.
Iran is currently under three sets of relatively mild UN Security Council sanctions for defying demands to halt uranium enrichment, which it says it needs purely for electricity generation.
The United States said Iran would now inevitably face tougher sanctions. Tehran brushed aside the warning.
At talks in Geneva on July 19, the six nations put forward a package of trade and nuclear technology incentives to Tehran, demanding a response within two weeks.
Iran's Islamic Revolution Guards Corps Commander Mohammad Ali Jafari reiterated Monday a threat to block the Strait of Hormuz, through which about 40% of global oil shipments pass, in the event of aggression against the country, the Fars news agency reported.
The U.S. and Israel have refused to rule out military action against Iran, the world's fourth largest oil producer, if diplomacy fails to end the dispute.
Iran recently conducted a series of missile test launches in the strait, which is located at the southern end of the Persian Gulf.
A Russian Foreign Ministry spokesman said Tuesday that deputy foreign ministers of the Iran Six could hold a phone conference on Wednesday to discuss the situation.
