The United Nations envoy to Sudan, Jan Pronk, says the Sudanese government recently lost two major battles against rebels in the Darfur region.
Writing on his personal website, Pronk says the losses occurred last month in Umm Sidir and last week in Karakaya. He says many soldiers were wounded in the battles and many taken prisoner.
Pronk also says morale among government soldiers in North Darfur has gone down, and that some have refused to fight.
The Sudanese government has not reacted to Pronk's comments. They were posted last Saturday but not widely reported until this week.
The latest violence involves the Sudanese government fighting a new Darfur rebel group known as the National Redemption Front. The rebel group claims that it won the clashes.
The Darfur conflict began in 2003 when rebels attacked government targets. The rebels accuse Khartoum of neglecting their region.
The rebels also accuse the government of favoring Arabs over black Africans.
More than three years of fighting in the region has killed some 200,000 people, and displaced 2 million others from their homes.
Some information for this report was provided by AP and Reuters.