US President Barack Obama's decision this week to pour 30,000 more troops into Afghanistan looks set to complicate Sino-US ties, forcing Washington to push Beijing harder to open its strategic border to the country and to co-operate over infrastructure investments. US officials say that Obama's most dramatic military move to date will be accompanied by a diplomatic offensive to draw in greater longer-term regional support for reconstruction efforts that will help stabilise Afghanistan once US forces start to withdraw in 2011. In the near term, China's short but vital border with Afghanistan on the mountainous Wakhan Corridor will get considerable attention as Washington seeks to open supply lines for its surge, which will see its forces expand to 100,000 troops. State Department spokesman Assistant Secretary of State Philip Crowley said that unlike Iraq, the Afghanistan mission was hampered by difficult supply lines that ran up through Pakistani ports. Insurgents have repeatedly attacked convoys. 'It remains of great concern to us,' Crowley told the South China Morning Post yesterday. 'We are looking at how to create alternative supply lines. This is something we will be talking to China and neighbouring countries about.' Speaking generally, he added: 'We are having discussions with China on Afghanistan and we want to see China play a constructive role.' The border issue has been raised previously with Beijing, most recently during Obama's first visit to China, but has yet to be approved. Afghan officials have also been pushing China to open the 73-kilometre border and consider building a railway and roads to improve links and trade. The panhandle-shaped corridor is close to territory held by insurgents and proved strategic in the 1980s as Beijing quietly assisted Washington in arming Afghan mujahideen during their fight against the Soviet Union's occupation. When asked about US requests over the corridor, Foreign Ministry spokesman Qin Gang said yesterday that negotiations were continuing but did not say any decisions had been finalised. Referring to the meeting between Obama and President Hu Jintao two weeks ago, Qin said: 'The statement made it clear that both sides support anti-terrorism activities in Afghanistan and the promotion of regional peace and stability.' Noting Obama's speech on Tuesday, Qin said China also hoped the international community would work towards that goal of long-term peace. 'China believes that Afghanistan's sovereignty, independence and territorial integrity should be fully respected. It will maintain communication and negotiations with United States regarding co-operation in the South Asia region, including Afghanistan,' he said. Speaking privately, however, other US officials warned of difficulties ahead, noting the sensitivities of Beijing over Afghanistan, which borders the restive province of Xinjiang , home to China's Muslim Uygurs. While Beijing would be happy to see the Muslim extremist Taliban movement and its al-Qaeda supporters crushed, it remains wary of the US-led operation in Afghanistan - now in its ninth year - and increasing numbers of foreign troops on its borders. Beijing has also been reluctant to allow US military flights or refuelling missions in Chinese airspace. In the longer term, however, Washington will also be seeking to work more closely with China over any planned aid or investments. Crowley said that while the intensifying military commitment was hogging the headlines, the effort of rebuilding Afghanistan infrastructure, institutions and economy would take a good deal of international co-ordination and co-operation. It involved everything from 'training judges ... to getting goods to market', he said. The US did not want to be leading an effort to impose any situation on Afghanistan from the outside, but wanted to build Afghans' capacity to run a fully functioning country. 'Ultimately, you defeat an insurgency by protecting [people], by improving their lives,' he said. 'This will take a great deal of international effort beyond the military aspect. 'Clearly China is playing a role in Afghanistan ... we would certainly like that to continue, not only with China, but also with Japan and Korea.' While the United Nations played a key co-ordinating role, the US wanted to explore other ways of co-operating as well to ensure aid and infrastructure work had 'maximum impact'. China's direct investment in its neighbour has been rising, peaking with a US$3.5 billion deal - Afghanistan's single biggest foreign investment - to operate a mine at Aynak, which sits above the second-largest reserve of copper in the world. China is building a hospital and mosque for local workers and will get half the output when production starts in 2011. Professor Rong Ying , of the China Institute of International Studies, said China had been active in reconstructive efforts in its neighbour long before US requests. Under bilateral deals, China had sent firms to build roads and irrigation systems and help train Afghan officials. He said it was too early to say what more China might do following US requests. The border involved both technical and practical questions. 'The US has long used the routes of Pakistan in the south, and Russia in the north, to transport supplies into Afghanistan,' Professor Rong said. 'These two are mature routes, unlike China's route which requires development.'