"We should not be over optimistic, but this is a chance to return to the negotiation table, said Steinmeier on Tuesday evening after meeting EU foreign policy chief Javier Solana who has presented the proposals to Tehran earlier in the day.

Iran should give its answer before June 29 when the G8 summit will be held in Moscow, said the minister. "That is the date people can wait for a decision," he added.

Solana described the talks with Iranian leaders as "constructive and good" and hoped that Iran may give an answer in the coming days. The process of solving the crisis remain in a "delicate phase", said Solana.

Earlier Tuesday after a two-hour meeting with Iranian leaders, Solana presented to Iran a package of incentives, which was agreed last week among five UN Security Council permanent members, Britain, China, France, Russia and the United States, plus Germany, in exchange for Iran's suspension of uranium enrichment.

Details of the proposals are unknown, but EU diplomats said they included a light-water nuclear reactor and a foreign supply of atomic fuel for Iran, as well as an offer to suspend sanctions against Iran in the UN Security Council.

The proposals also carry penalties that can be applied by the United Nations Security Council if Tehran does not cooperate, said the diplomats.

Iran's chief nuclear negotiator Ali Larijani said the talks with Solana were "constructive" and the proposals contained some "positive steps" but some "ambiguities" had to be removed.

Speaking on the state television after receiving the proposals, Larijani said Iran would respond after studying the incentives.