Presenting a united front in effort to restrain Iran's nuclear energy program, U.S. President Barack Obama and Russian leader Dmitry Medvedev warned Sunday that they were losing patience with Tehran and will not wait much longer for it to accept a diplomatic proposal to resolve the dispute. After an hourlong private meeting in Singapore, on the sidelines of an Asia-Pacific group summit, the two leaders expressed dissatisfaction with Iran's response to a proposal to ship its enriched uranium abroad to be turned into fuel for a Tehran medical reactor. In Geneva last month, Iran agreed to the deal in principle, but U.S. officials said Iranian leaders have since thrown up obstacles. 'Unfortunately, so far at least, Iran appears to have been unable to say yes to what everyone acknowledges is a creative and constructive approach,' Obama said after the bilateral meeting, calling the offer to Iran a fair one. If Tehran is defiant, Obama said, 'the alternative would be an approach that would involve increasing pressure on Iran to meet its international obligations.' Medvedev, for his part, said, 'We're still not satisfied with the pace of advancement of the process.' Although other Russian leaders, notably Prime Minister Vladimir Putin, have been less enthusiastic about the prospect of increased economic sanctions, U.S. officials said the deadline for Iran to act is the end of the year. The U.S. and Russia hope the threat of new sanctions will be enough to win agreement from Iran, and officials said the two leaders discussed a timetable for possible actions during their meeting Sunday. The U.S. and many other Western powers believe Iran is seeking to develop nuclear weapons; the proposal would diminish Iran's stockpile of nuclear fuel below the level needed for making a single nuclear weapon if further enriched. Iran insists its nuclear development program is for civilian energy purposes only. Sunday, Michael McFaul, a senior adviser to Obama, told reporters: 'Both presidents said time is running out. And therefore we have to make preparations now to deal with the contingencies should the Iranians decide they don't want to be serious about the diplomatic path.' After meetings with Medvedev and other Asia-Pacific leaders in Singapore, Obama left for Shanghai on the start of a three-day visit to China that marks the heart of his inaugural trip to Asia. China is Iran's largest trading partner, and Obama will have his work cut out in persuading Beijing to apply additional pressure on Tehran. No Iranian official reacted immediately to the comments in Singapore. But the powerful speaker of Iran's parliament on Sunday delivered some of his harshest words yet against Obama, who took office vowing to attempt to use diplomacy to overcome decades of hostility between Tehran and Washington and forge a deal on the nuclear program. Ali Larijani criticized the Obama administration for extending sanctions against the Islamic Republic for another year and seizing the U.S. assets of the Alavi Foundation, an Islamic charity. 'One year after making hollow speeches and slogans, it is disgraceful that the attitude of the U.S. president was nothing different from that of his predecessor,' Larijani said in an address to lawmakers, according to the official Islamic Republic News Agency. 'All these acts indicated that Obama's alleged changes were nothing more than a deceptive symbol for stupid politicians.' The U.S. and international arms inspectors continue to await a definitive response to a proposal to transfer the bulk of Iran's nuclear fuel to Russia and France to be further refined and fitted for the medical reactor. Larijani, who has described the nuclear fuel swap proposal as against Iran's interests, dismissed such a deal as 'unacceptable.' French foreign minister Bernard Kouchner told an Israeli newspaper Sunday that his nation had grown pessimistic about the prospect for a deal. 'In effect the answer has almost been given already, and it is negative,' he told the daily Yedioth Ahronoth. 'That's a shame, a shame, a shame.' He added, 'We are waiting. This is not good, and very dangerous.' In their private meeting, Obama and Medvedev also discussed arms control between their two nations, which are negotiating a nuclear arms reduction treaty that would succeed one that is set to expire early next month. White House officials said they expected to reach an agreement that would keep arms control arrangements in place until they forged a new accord to replace the Strategic Arms Reduction Treaty, which would need to be ratified by the U.S. Senate and the Russian Duma. In recent weeks, Ellen Tauscher, a U.S. undersecretary of State for arms control, has expressed disappointment over the Russian response to an offer put forward by the U.S. After the meeting, Obama voiced confidence they will meet the Jan. 1 deadline 'if we work hard and with a sense of urgency about it.' Obama and Medvedev joined other leaders of the 21-member Asia-Pacific Economic Cooperation group meeting for discussions on a wide range of economic and social issues. For Obama, the visit and meetings in Asia are part of a broader effort to engage in a region that many feel has been largely neglected by the U.S. -- even as China, an emerging global superpower, has significantly increased its influence. Obama's agenda includes pressing for a shift in Asian economic policies to buy more American goods as well as laying out his vision on nonproliferation, the environment and human rights. So far, he has not come away with much in the way of tangible results. In Singapore, Obama and other world leaders conceded that it was unlikely that negotiators could achieve a binding accord to limit climate change at an international conference next month, and as such agreed that they should instead focus on a more limited agreement. Obama will be discussing climate change with his Chinese counterpart, Hu Jintao, during his two-day visit in Beijing. Obama is also expected to raise two other sensitive topics with Hu -- Chinese currency policy and human rights. In Singapore, the U.S. was met with criticisms of protectionism from Mexico and other parties, and the statement issued by the Asia-Pacific Economic Cooperation at the conclusion of the summit did not include reference to currency exchange policies, something that was resisted by Chinese officials. Many analysts on both sides of the Pacific believe China's currency is significantly undervalued and as such gives Chinese exports an advantage in selling to overseas markets. In his major Asia speech delivered in Japan, Obama spoke about the importance of human rights, but he did not mention Tibet or other specifics related to China. The president did cite his concerns about the regime of Myanmar, and during a meeting in Singapore with the Association of Southeast Asian Nations, which includes Myanmar, White House officials said Obama reiterated his call for the release of opposition leader Aung San Suu Kyi. The ASEAN group's joint statement, however, made no mention of releasing Suu Kyi, although it called for free, fair and transparent elections in Myanmar next year. Nicholas reported from Shanghai and Singapore, Daragahi from Beirut; staff writer Don Lee in Washington and special correspondent Jean Yung in Shanghai contributed. 