Andrew Natsios told a news conference that the bombing restarted after a lull from the beginning of February to the end of April.
"This should end and the crease-fire that was agreed to sometime ago should be respected," he said, according to Reuters. "We urge the Sudanese government to end all bombing in Darfur immediately."
The Sudanese government signed a cease-fire with the two main rebel groups in Darfur, the Justice and Equality Movement and the Sudan Liberation Movement, in 2004, though violence has continued.
Another peace deal was signed by one rebel group in May 2006. Since then, the rebel groups have split into many more factions.
Natsios said the bombings targeted the Jebel Marra region, a stronghold of Abdul Wahid Mohammed Nour, leader of one of the Darfur rebel groups, Reuters reported. And he said he thought other bombings were occurring in the western and northern parts of Darfur.
The Sudanese government could not be reached for immediate comment, according to Reuters.
The report came a day after Sudan's Ministry of Justice Undersecretary Abduldaim Zamrawy told the U.N. Human Rights Committee that Khartoum was "carrying out its duty to protect civilians in Darfur."
Fighting between the rebel groups in Darfur and Janjaweed militias, which many believe are backed by the government, has led to the deaths of at least 200,000 people and displacement of 2 million to refugee camps.
After intense international pressure, Sudan agreed last month to a combined U.N.-African Union peacekeeping force of 20,000. About 7,000 AU forces are operating in Darfur, but the violence has continued.
A resolution circulating in the U.N. Security Council would allow the United Nations to formally recruit troops for the mission. A vote is expected later this month.