"Two of our military were killed and three AU military were wounded, and two civilian personnel were killed," Jean Baptiste Natama, acting head of the AU mission in Sudan said, adding the ambush took place in South Darfur state on Saturday.
"We are investigating, but it is serious being the first time our personnel are killed in Sudan," Natama said, adding there were no details on who was behind the attack.
About 6000 AU troops are deployed to monitor a shaky ceasefire in the region but violence has escalated in recent weeks, prompting the AU last week to voice its harshest public criticism of Darfur rebels and the Sudanese government.
A senior AU official accused all sides of ignoring all deals signed so far and said the government had used disproportionate force targeting civilians in the remote region, where more than two million have fled their homes and live in wretched camps.
Samani Wasiyla, Sudan's state minister for foreign affairs, said he did not know who was responsible for the ambush but that it was definitely not government troops.
"It is unfortunate that there has been casualties," he said. "I want to assure all that the government is committed to seeing that the mission of the African Union forces succeeds."
"I want to assure all that the government is committed to seeing that the mission of the African Union forces succeeds"
Sudan minister for foreign affairs
The ambush of the AU patrol on Saturday happened near Khor Abeche, where government-backed militias wiped out a rebel base earlier this year.
South Darfur was the scene of a rebel attack on a government garrison last month, which sparked a wave of tit-for-tat violence.
A sixth round of peace talks began last month to try to end the revolt that has killed tens of thousands in Sudan's remote west. Rebels accuse the central government of neglect and of monopolising wealth and power.