Amnesty International on Thursday accused Myanmar's military of committing crimes against humanity in ethnic conflict zones, where ongoing fighting has overshadowed sweeping political changes.
The rights group also alleged that authorities had blocked humanitarian aid from reaching tens of thousands of desperate refugees in conflict areas and said soldiers had sexually assaulted civilians.
"The government enacted limited political and economic reforms, but human rights violations and violations of international humanitarian law in ethnic minority areas increased during the year," Amnesty said in its annual report.
"Some of these amounted to crimes against humanity or war crimes."
The Myanmar army had launched "indiscriminate attacks" that at times targeted ethnic minority civilians, it said.
In northern Kachin, where a decades-old conflict erupted again last year, there were reports of extrajudicial executions, shelling that killed children, forced labour and unlawful destruction of food and property, it said.
In neighbouring Shan state, civilians were tortured, arbitrarily detained and forcibly relocated, according to Amnesty.
"Soldiers reportedly sexually assaulted Kachin and Shan civilians," it added.
There were credible accounts of the army using prison convicts as porters, human shields and mine sweepers, it said.
Myanmar's quasi-civilian government has agreed ceasefires with several armed ethnic minority groups since coming to power last year, raising hopes of an end to civil war that has gripped parts of the country since independence in 1948.
But a series of meetings with the rebels fighting in Kachin, where a 17-year ceasefire was shattered last year, have failed to end the violence there.
The reformist regime recently overhauled its negotiating team, putting the president at the helm of the process and removing some elements of the previous delegation seen by Kachin rebels as linked to army hardliners.
President Thein Sein's government has won international praise for releasing hundreds of political prisoners and welcoming pro-democracy leader Aung San Suu Kyi and her party back into mainstream politics.
An end to the conflicts and alleged rights abuses are key demands of the international community, which has begun to roll back sanctions.