China's involvement in Sudan stretches back more than a decade and has snowballed to the extent that it now supplies nearly a quarter of the African country's imports and accounts for about 70% of its exports, mostly oil.
But despite growing global criticism of Chinese blank cheques written to the regime in Khartoum, Beijing has shifted its policy in the past 18 months. Though President Hu Jintao announced a $13m interest-free loan for a new palace for his Sudanese counterpart, Omar al-Bashir, and cancelled debt worth $70m during a visit to Sudan in February last year, his government publicly called for a ceasefire and a negotiated settlement in Darfur.
A special envoy, Liu Guijin, was later appointed to help find a political solution in Darfur, and a team of 300 engineers was committed to support the peace effort.
Most significantly, analysts say, China backed security resolution 1769, which nearly tripled the size of the peacekeeping force in Darfur to 20,000 and brought in the UN alongside the African Union, which had led the mission. After successfully lobbying Bashir to accept the new force, China announced a $10m contribution to humanitarian aid in the country.
But many experts question how much pressure China is really exerting. Although the Chinese delegation at last month's African Union summit warned that the world was "running out of patience on Darfur", Sudan's government continues to hamper the new peacekeeping mission's deployment, and last week launched the heaviest aerial attacks on villages in Darfur for more than a year.
"Sudan does listen and will continue to listen to what China says," said Sally Chin, Sudan analyst for the International Crisis Group. "There is so much more that it could be doing to put pressure on Khartoum to allow in the peacekeepers into Darfur, and to respect the ceasefire."
Egbert Wesselink, head of the European Coalition on Oil in Sudan, a research group, said China's "positive" influence did not appear to have had any real effect.
"It may be that it is giving a lot of good and wise advice to Sudan in private, but I have yet to see any tangible results in Darfur. So is this 'new Chinese policy' meaningful? I would have to say not."
The relationship stretches back to 1994, when Khartoum's role in sponsoring terror and waging civil war in the south of the country severely limited its options for developing its petroleum industry. Eager to crack the western-dominated oil market, China dived in, helping Sudan become an oil exporter within five years by building a 1,000-mile pipeline and a refinery in the capital. Along the way, the state-owned Chinese National Petroleum Company took 40% stakes in Sudan's two main oil consortiums.
For China this proved extremely profitable as oil prices soared; in Sudan, human rights groups say, it helped fuel wars. The Swiss-based Small Arms Survey says that up to 80% of Sudan's share of its early oil revenues was spent on weapons for the war in the south - with the close assistance of China, which had previously sold it fighter jets and military helicopters. By the beginning of the separate Darfur conflict in 2003, China had overtaken Iran as the country's main arms supplier and helped build weapons factories in Sudan.
For Khartoum, which has also benefited from soft loans and Chinese expertise in building dams, bridges and rail networks, the partnership had another crucial upside. As the war in Darfur attracted increasing international condemnation, China used its permanent seat on the UN Security Council to consistently stop strong action being taken against Sudan.