The report by Kofi Annan, the UN secretary-general, came amid reports of more fighting in the region that has left more than 60 people dead, and amid a denial by the Sudanese government that it has broken a ceasefire.
Annan said in the report released on Monday: "Civilians in Darfur continued to suffer the consequences of persistent violence and insecurity."
Government embargoes on goods entering areas of Darfur held by the rebel Sudanese Liberation Army "have prevented the access of civilians to vital goods and constitute a violation of international humanitarian law," Annan wrote.
The report covered the months of March and April but made clear that a May 5 peace deal signed between Sudan's government and a main rebel faction has done little to bring solace to civilians in Darfur, where fighting has killed nearly 200,000 people and displaced 2.5 million since 2003.
Annan accused all parties in the conflict of also violating humanitarian law with "totally unacceptable levels of violence and despicable attacks against civilians", even as final negotiations for the peace deal took place.
Annan's report came as African and UN officials reported more fighting in Darfur with armed factions seeking more territory ahead of a planned disarmament.
"Civilians in Darfur continued to suffer the consequences of persistent violence and insecurity"
Moussa Hamani, chief information officer for the African Union in Sudan, said: "The problem seems to be that everyone wants to maximise their territory before the truce and disarmament actually come into effect."
Scattered fights have erupted in recent days in southern Darfur, where Sudan's army and police have said they would disarm bandits, according to UN and African Union officials.
Nomadic tribal militia, known as Janjawid, launched two attacks on Friday that killed 35 villagers, Hamani said on Sunday.
In a separate incident on Friday, villagers attacked a Janjawid militia in the southern Darfur area of Kalaka. The fighting killed 11 farmers and eight Janjawid, the United Nations said.