A THAW in relations between the US and China appears to be under way after months of strain between the two superpowers over arms sales to Taiwan, cybersecurity, the Dalai Lama and the massive trade imbalance.

The Chinese foreign ministry announced on Thursday that President Hu Jintao is to visit Washington on April 12-13 for a nuclear proliferation summit. The decision came less than 24 hours after it emerged that China, after months of stalling, had agreed to engage in negotiations on drafting UN sanctions against Iran.

The visit by Hu was regarded as a litmus test for the state of relations by Washington, which feared he might boycott the summit in protest over arms sales to Taiwan and other causes of tension.

The Chinese foreign ministry spokesman, Qin Gang, hinted at a thaw on Thursday when he told reporters “I'd like to reiterate that the undue disruption which China-US relations endured not long ago is in the interest of neither country and is not what we would like to see.”

Obama had kind words, too, for China when he met the new Chinese ambassador to the US this week, and which were widely reported by the Chinese media as reflecting a positive change on the part of Washington.

But there are potential problems looming, the biggest of which is whether the US treasury will cite China for manipulating its currency in its annual report on April 15, days after Hu's visit.

Analysts in Washington said that China may have secured a promise from the US that it would not be cited as a quid pro quo for attending the summit and the deal on Iran.

The apparent thaw marks another success for Obama, who has seen his fortunes improve on both the domestic and foreign policy fronts since winning the protracted struggle to secure health reform in the US.

Kenneth Lieberthal, a China specialist at the Washington-based Brookings Institution and a former special adviser on Asia in the Clinton White House, said that the rough patch looked to be over. “I have been expecting an uptick in relations and I think that is what we are seeing. I would give Obama credit. I think China tested Obama over the Dalai Lama and Taiwan and the administration was firm,” Lieberthal said.

He saw the move on Iran as a positive step, showing that China was prepared to engage in serious negotiations. “They are making it clear they are now in the game,” he said. “They are very concerned about proliferation in the Middle East. The question is what they are going to do about it.”

As well as the visit in a fortnight, discussions are underway between Beijing and Washington about a state visit to the US by Hu, possibly in June, returning the courtesy of Obama's visit to China in November.

Obama, the most Pacific-orientated president yet, regards US relations with China as having the potential to define the 21st century, and reached out to Beijing last year, bringing accusations from Republicans that he was being too soft.

Beijing tested Obama for weakness earlier this year, complaining more vociferously than normal about US arms sales to Taiwan and over the visit to the White House by the Dalai Lama. The US secretary of state, Hillary Clinton, embarrassed Beijing with a speech expressing opposition to Chinese Internet censorship, an issue highlighted last week by Google's decision to in effect shut down its mainland China operation.

The US, Britain, France and Germany have been trying since late last year to put together a package of new sanctions against Iran, which they claim is intent on securing a nuclear weapons capability. But China, which has economic ties to Tehran, has proved reluctant to take punitive action.

The shift took place during a telephone conference between the five countries, plus Russia, on Tuesday.

— The Guardian, London