MOSCOW (AFP) - Afghanistan is a "very productive area" for engagement between Washington and Tehran, a US official said Friday at a meeting in Moscow aimed at curbing rising violence in the conflict-riven nation. The meeting, led by the Shanghai Group comprising China, Russia and Central Asian states, came amid mounting international concern over the resurgence of the Taliban militants in Afghanistan. "We see Iran as an important player related to Afghanistan. We see this as a very productive area for engagement in the future," the US official, who asked not to be named, said on the sidelines of the conference. The United States and Iran have had no diplomatic ties for almost three decades but President Barack Obama in a message on March 20 offered to end the animosity, in a departure from the previous administration's tough line. Iranian Deputy Foreign Minister Mohammad Mehdi Akhonzadeh, who was leading the delegation from Tehran, reaffirmed his government's line that Washington needed to change its policies before changes could take place. "The United States should change its attitude and it should be measurable. It can use rhetoric but those changes must be felt. There is need for real change that can be measured," he told AFP. The Moscow meeting is also being attended by UN chief Ban Ki-moon, Shanghai Group observers, Nato officials, delegates from Afghanistan and Iran as well as representatives of the G8 group of leading industrialised countries. The US sent Deputy Assistant Secretary for South and Central Asian Affairs Patrick Moon to the conference but he did not meet Iranian delegates. The meeting comes ahead of another international conference on Afghanistan in The Hague on March 31, due to be attended by US Secretary of State Hillary Clinton and other top diplomats. In a final declaration, the Moscow meeting's participants emphasised "the need for sustained international support to strengthen Afghan security institutions to effectively combat the scourges of terrorism and production and trafficking of narcotics." Meanwhile, top US lawmakers urged President Barack Obama in a letter Friday to open talks with Iran "as soon as possible," but warned they must yield quick results on the West's nuclear dispute with Tehran. "Engagement must be serious and credible, but it cannot be open-ended," the group, which included chairman of key House committees, wrote in the letter amid growing signs of Washington outreach to the Islamic republic. The lawmakers said the central goal of any talks must be to get Iran to verifiably suspend uranium enrichment - a possible prelude to a nuclear weapon - "within at most a few months of the initiation of discussions." They said US outreach "cannot be deferred" until after Iran's June presidential elections and said Washington and its allies must be prepared to impose a range of painful economic sanctions in Iran pursues enrichment. "We urge that the talks begin as soon as possible, so that we will have the earliest possible indication of whether they will succeed in halting Iran's nuclear program," they wrote in the message. Obama must be prepared to consider moves like slapping sanctions on Iran's central bank, punishing international banks that do business with Iranian banks, targeting energy firms that invest in Iran's oil and gas sector, and closing US ports to shipping companies that call on Iranian ports. US allies "should be prepared to prohibit Iranian banks from operating on their territory and to cease allowing Iran to conduct international financial transactions in Euros, pounds, and yen," the lawmakers wrote. US allies must also stop providing export credits to firms seeking to do business in Iran, and bar exports of refined petroleum and catalytic converters to the Islamic republic, they said. The seven lawmakers also urged Obama to "make Iran a matter of the highest priority in our relations with Russia and China. The group included Democratic House Majority Leader Steny Hoyer, as well as the Democratic chairmen of the House Foreign Affairs, Armed Services, and Intelligence Committees. "If we truly mean that Iran cannot be allowed to possess nuclear weapons, urgent action is required today. We must use the time available to us to begin engagement and to convince the Iranians of our seriousness of purpose. Otherwise, we will face far more difficult decisions in the future," they said.