The United Nations High Commissioner for Human Rights said on Friday of that violence in Myanmar is intensifying and condemned the army's "outrageous" use of heavy weapons, while urging a wider diplomatic effort to pressure the ruling generals.
Michelle Bachelet said the junta had shown no willingness to implement a five-point consensus it agreed with the Association of Southeast Asian Nations (ASEAN) in April to halt violence and start dialogue with its opponents.
Bachelet said there were credible reports that in Kayah State, civilians were being used as human shields and the army was shelling homes and churches, which had forced more than 108,000 people to flee, with little food, water or sanitation, and humanitarian access was blocked, reports Reuters.
"There appear to be no efforts towards de-escalation but rather a build-up of troops in key areas, contrary to the commitments the military made to ASEAN to cease the violence," Bachelet said in a statement.
Myanmar has been in turmoil since a Feb 1 coup ousted Aung San Suu Kyi's elected government, unleashing daily protests and strikes that have paralysed the economy, and fighting in borderlands between the armed forces and ethnic minority guerrilla forces and militias.
A junta spokesman did not immediately respond to calls seeking comment.
The Southeast Asian mediation effort has made little progress. ASEAN's foreign ministers, China and Japan were among several countries this week stressing the importance of the peace plan being implemented.
The United Nations, Western countries and China all back the ASEAN effort, but the Myanmar military, known as the Tatmadaw, has paid little heed to that and instead touted the progress of its own five-step plan towards a new election.
Bachelet encouraged the intensification of diplomacy, including from influential states, and said dialogue was urgently needed with all political stakeholders, including a shadow government made up of opponents of military rule.
Two ASEAN envoys visited Myanmar last week and met top junta officials, including military chief Min Aung Hlaing, a trip that was criticised by pro-democracy groups, who say they are being shut out.
"The international community needs to unify in its demand that the Tatmadaw cease the outrageous use of heavy artillery against civilians and civilian objects," Bachelet said.
"The military leadership is singularly responsible for this crisis, and must be held to account."
She also said newly formed civilian forces, known as People's Defence Forces, and other armed groups, must take all measures to keep civilians away from harm.
Bachelet also said she was deeply troubled by detentions and reports of torture.
According to the Association for Political Prisoners (AAPP) activist group, 5,965 people been arrested since the coup. Of those, 4,804 remain in prison, interrogation centres, and under house arrest.
At least 860 people have been killed, 22 of those from torture during detention, the AAPP says.
The junta has branded its opponents terrorists and outlawed many organisations, including the AAPP.
The state-run Global New Light of Myanmar newspaper gave a breakdown on Friday of offences committed since the military took power.
It included 49 held for arson and terrorist acts and 61 suspected of murder, 256 people arrested for illegally holding arms and 272 for terrorism and destructive acts.
Among the weapons seized were 914 homemade guns, 50 small arms, and 5,947 homemade bombs, the paper said.