Although Western democracies have praised the government for political reforms in the past year, the military has been conducting an offensive against the Kachin Independence Army (KIA) with 160 battalions since June, displacing up to 75,000 civilians of the Kachin ethnic minority.
"While things may have changed in Burma, the kind of abuses we uncovered in this report were very similar to the kind of abuses meted out by the Burmese army during much of its post-colonial existence," said Phil Robertson, Human Rights Watch's Thailand director.
The government signed ceasefires with a half-dozen other ethnic minority rebel groups this year but has not made a peace pact with Kachin guerrillas fighting for autonomy in their traditional territories in northern Burma for the past six decades.
"It is unmistakably an ethnic war," said Matthew Smith, one of the report's authors.
"One of the more serious findings was that the Burmese army has attacked civilians," he said, citing evidence of the extrajudicial execution of at least three civilians.
Both sides were using antipersonnel mines and forced labour on the front lines, including children as young as 14, Human Rights Watch said after 100 interviews with refugees and aid workers.
It also accused the army of rapes and other sexual violence.
"Concerned governments should urgently support an independent international mechanism to investigate abuses by all sides to the conflict in Kachin State and in other ethnic areas," said Elaine Pearson, deputy Asia director for Human Rights Watch.
The greatest threat to Kachin refugees is their lack of access to humanitarian aid, the report said.
"This is a decision by the Burmese government, not the Burmese army," Robertson said.
Some observers have claimed that the army, which has sustained heavy casualties in Kachin State, was acting independently of the government in its ongoing offensive.
Human Rights Watch acknowledged that both sides in the conflict had blocked aid to about 45,000 refugees who have fled to 30 camps in under the control of the Kachin Independence Organization (KIO), the political arm of the KIA, on the Burma-China border.
The government granted UN agencies access to the area in December, but has reportedly denied access since.
The KIO on at least one occasion rejected the delivery of humanitarian aid from the Kachin State Rescue and Resettlement Committee and the Red Cross, the report said.
"There's still a long way to go before the people of Burma, particularly those in conflict areas, benefit from recent promises of reform," Pearson said. "The international community should not become complacent about the serious human rights violations still plaguing Burma."