BRUSSELS (AFP) - EU foreign policy chief Javier Solana received a letter from Tehran Tuesday, and will discuss its contents with the six world powers involved in talks on Iran's nuclear programme, his office said. "We have received the letter," a member of Solana's team told AFP. "It will be studied," he added, without giving any details on the contents. " Solana will discuss it with representatives of the five-plus-one" on Wednesday (today), he added, referring to the five permanent UN Security Council members plus Germany, involved in the nuclear talks with Iran. Earlier a source with Iran's Supreme National Security Council told AFP the message did not contain the final response to an incentive package offered by the six powers in exchange for a uranium enrichment freeze. Another source from the Iranian Security Council said the message was no more than a transcript of a telephone conversation between Solana and Iran's top nuclear negotiator Saeed Jalili on Monday. The United States said the world powers would discuss their next move on Wednesday and indicated that Tehran faced a fourth set of UN Security Council sanctions if it failed to give a positive response. The six world powers had offered Iran negotiations on a package of technological incentives if it suspends the sensitive process of uranium enrichment, which the West fears could be used to make nuclear weapons. Tehran has steadfastly refused to suspend its uranium enrichment activities, which it says are only aimed at producing fuel for nuclear power for a growing population. The United States said Iran faced "additional measures" if it did not respond clearly. "If we are not going to receive a clear response, a clear message from them, we are going to have no choice but to pursue additional measures," US State Department spokesman Gonzalo Gallegos said. Negotiators from the six powers - United States, Britain, France, Germany, Russia and China - have scheduled a conference call for tomorrow, the spokesman said. Along with the threat of further sanctions, Washington has warned that the option of military action against Iran remains open if Tehran sticks to its defiant line. Amid the continued tensions, Iran said on Monday it had successfully test-fired an anti-ship missile with a range of 300 kilometres (180 miles) that would allow it to close the Strait of Hormuz between Iran and Oman.