The US expressed hope Wednesday that the package of proposals Iran presented to world powers to resolve the nuclear standoff would be serious and constructive. "We hope that what is contained in that response is a serious, substantive and constructive response to the P5 + 1 proposal," US Ambassador to the United Nations Susan Rice told reporters after a UN Security Council meeting. "We will study the content carefully." Foreign Minister Manouchehr Mottaki gave a package of proposals to diplomats representing the five permanent members of the UN Security Council and Germany in a meeting in Teheran attended by journalists. He announced no details of the package. The proposals came as the UN nuclear watchdog agency was holding a meeting in Vienna, Austria. US President Barack Obama and European allies have given Iran until the end of September to take up an offer of nuclear talks with six world powers and trade incentives should it suspend uranium enrichment. If not, Iran could face harsher punitive sanctions. But Iranian President Mahmoud Ahmadinejad said Monday that Iran considered the nuclear issue closed and rejected any halt to enrichment. He said Iran was proposing to hold negotiations over a range of "global challenges," but the only nuclear issues that it was willing to discuss were mechanism to ensure the global use of peaceful nuclear energy, to promote disarmament and to halt nuclear proliferation. The US and some its allies believe Iran is secretly trying to build a nuclear weapon, an accusation denied by Iran, which says it aims only to generate electricity. The United Nations has demanded Iran halt enrichment, a process that can produce fuel for a reactor or the material for a warhead. Iran says it has a right to pursue enrichment for fuel. The US, Britain, France and Germany urged Iran on Wednesday to hold talks to reach a comprehensive diplomatic solution to the international standoff over its nuclear program.