Myanmar's Government has dismissed allegations by the departing United Nations rights envoy that the military was committing fresh war crimes in Rakhine state as "biased", blaming rebels for violations.

"We found that her investigation has no balance and was biased," Government spokesman Zaw Htay told a press conference.

Yanghee Lee, whose formal title is special rapporteur, called for a new investigation into allegations of war crimes and crimes against humanity during recent fighting in the South-East Asian country.

She said the basis for her conclusion was that the armed forces, known as the Tatmadaw, have ramped up attacks against civilians in recent weeks with air and artillery strikes.

"While the world is occupied with the COVID-19 pandemic, the Myanmar military continues to escalate its assault in Rakhine state, targeting the civilian population," Ms Lee said in a statement issued on Wednesday in Geneva.

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Ms Lee accused Myanmar's military of "inflicting immense suffering" on ethnic minorities in Rakhine and Chin states, where the government is battling the Arakan Army, a well-armed and well-trained guerrilla force representing the Buddhist Rakhine minority.

Dozens have died and tens of thousands have been displaced in the region in recent weeks.

"It's really hard to believe they're not targeting civilians," Ms Lee said this week. The Tatmadaw has denied it has targeted civilians.

Ms Lee, a South Korean whose term ends this month, has been a sharp critic of Myanmar's military since her appointment in 2014, focusing especially on human rights abuses against the Muslim Rohingya minority in Rakhine state.

In an interview with Al Jazeera, Ms Lee was scathing in her assessment of former human rights hero Aung San Suu Kyi, saying she was "utterly disappointed" with the performance of Ms Suu Kyi's democratically elected Government since 2016.

In August 2017, the Tatmadaw launched what it called a clearance campaign in northern Rakhine state in response to attacks by a Rohingya insurgent group.

The campaign forced more than 700,000 Rohingya to flee to neighbouring Bangladesh. Security forces were accused of mass rapes and killings and burning thousands of homes.

The International Court of Justice in the Netherlands agreed last year to rule on charges of genocide lodged against Myanmar.

Bangladesh's coast guard last month rescued 396 starving Rohingya refugees who had been drifting at sea for weeks after failing to reach Malaysia. At least 32 had died.

It has sparked fears of a repeat of the 2015 Andaman Sea Crisis, when around 8,000 Rohingya were stranded at sea by smugglers, killing hundreds.

ABC/wires