Two senior U.S. officials on Wednesday praised China for increasing pressure on Sudan to change its behavior in Darfur but said Beijing can do much more to stop Khartoum from harming civilians in the Sudanese region.

Thomas Christensen and James Swan, deputy assistant secretaries of state for East Asia and Africa, respectively, also told lawmakers that the U.S. is pushing China to reconsider its close military ties with "repressive regimes on the continent."

The officials said in joint prepared testimony that China's support of Zimbabwe's Robert Mugabe, and others "who rule through guns and intimidation, harms China's image and undermines its ability to play the role of responsible stakeholder in Africa's affairs."

Christensen and Swan said China has voted for a U.N.-African Union peacekeeping mission in Darfur and pledged to send up to 300 military engineers to the region, where conflict has killed more than 200,000 people and resulted in more than 2.5 million displaced people or refugees.

But the officials also told the Senate Foreign Relations Subcommittee on Africa that the U.S. is asking Beijing to stop Chinese companies' "substantial arms trade" with Sudan because the weapons are likely being used by the government in Darfur.

Sen. Russ Feingold, D-Wis., said that the world should not tolerate "reckless behavior" from China, such as "when they sell weapons to Sudan that can be used to prolong the conflict in Darfur, or build new power plants that support Robert Mugabe's repressive regime in Zimbabwe."

China defends its efforts to stop violence in Darfur and has suggested that Western countries which condemn China's oil interests in Sudan are being hypocritical.

Energy-hungry China buys two-thirds of Sudan's oil output. Critics regularly urge Beijing to use its economic leverage to push Sudan's government more strongly to make peace in Darfur.

The two U.S. officials testified that, despite popular assumptions, China's large oil companies are not big players in Africa's energy industry, with the exception of Sudan.

They said that total output in Africa in 2006 by all Chinese producers was about one-third of that of a single U.S. firm, ExxonMobil.

The Darfur conflict began in 2003, when ethnic African rebels took up arms against the Arab-dominated central government, accusing it of discrimination. Khartoum is accused of retaliating by unleashing janjaweed militias, blamed for the worst atrocities against civilians. The government denies the accusations.