The United Nations human rights investigator on Myanmar said on Thursday the military junta had "murdered" at least 70 people since its Feb. 1 coup, perpetrating killings, torture and persecution that may constitute crimes against humanity.

More than half of those killed were under the age of 25, Thomas Andrews told the UN Human Rights Council in Geneva.

More than 2,000 people have been unlawfully detained since the military seized power and the violence is steadily increasing, he said.

"The country of Myanmar is being controlled by a murderous, illegal regime," said Andrews.

"There is extensive video evidence of security forces viciously beating protesters, medics, and bystanders. There is video of soldiers and police systematically moving through neighbourhoods, destroying property, looting shops, arbitrarily arresting protesters and passersby, and firing indiscriminately into people’s homes."

Chan Aye, permanent secretary of Myanmar's foreign affairs ministry, said that authorities have been focused on maintaining law and order. "The authorities have been exercising utmost restraint to deal with violent protests," he said.

Andrews, a former member of the US Congress, speaking by video message from Washington, DC, said that basic rights to freedom of expression and assembly are being denied in Myanmar.

He called for imposing multilateral sanctions on the junta leaders and on the military-owned Myanmar Oil and Gas Enterprise, whose revenues from natural gas projects he said were set to reach $1 billion this year.