Mr Mahn Win Khaing Than, who is on the run along with most senior officials from the ruling National League for Democracy Party, addressed the public via Facebook on Saturday, saying: "This is the darkest moment of the nation and the moment that the dawn is close".
This handout photo taken on March 8, 2021 and released on March 9 by the Myitkyina News Journal shows a nun pleading with police not to harm protesters in Myitkyina in Myanmar's Kachin state, amid a crackdown on demonstrations against the military coup.
An estimated 3,000 people were killed when the army crushed the uprising, at the time the biggest challenge to military rule dating back to 1962.
In the commercial capital Yangon, hundreds of people demonstrated in different parts of the city after putting up barricades of barbed wire and sandbags to block security forces.
"Two were killed - with one shot in his head and another one hit with a shot that penetrated his cheek to the neck", he said, adding that they had to wait until the police stopped shooting to retrieve the bodies.
A truck driver in Chauk, a town in the central Magwe Region, died after being shot in the chest by police, a family friend said.
Soldiers have been occupying hospitals and universities across Myanmar as they try to quash a civil disobedience movement that started with government employees such as doctors and teachers but has expanded into a general strike that has paralyzed many sectors of the economy.
At least 13 people were killed on Saturday, one of the bloodiest days since the Feb 1 coup, witnesses and domestic media said.
Suu Kyi emerged as a democracy icon during the movement and was kept under house arrest for almost two decades.
Security forces have been using increasingly brutal tactics to suppress a nationwide protest movement opposing the military takeover of the democratically elected government on February 1.
Suu Kyi's National League for Democracy party led a return to civilian rule with a landslide election victory in 2015, and an even greater margin of votes past year.
This year, the generals overthrew her government and detained Suu Kyi and many of her cabinet colleagues, claiming fraud in the November elections.
"As longstanding supporters of Myanmar and its people, we emphasise the urgent need to restore democracy and the priority of strengthening democratic resilience", the four leaders said in a statement released by the White House.
The UN's Special Rapporteur on human rights in the country, Thomas Andrews, gave a bleak assessment of the crisis.
Myanmar is "controlled by a murderous, illegal regime" that is probably committing "crimes against humanity", Andrews told the UN Human Rights Council in Geneva.
The US government said yesterday that Myanmar citizens stranded by the violence following the country's military coup would be able to remain inside the United States under "temporary protected status".
In condemnation of the actions taken by Myanmar's military, Director of Foreign Assets Control Andrea Gacki said, "The indiscriminate violence by Burma's security forces against peaceful protesters is unacceptable".
The coup in Myanmar, where the military has close ties to China, is a major early test for US President Joe Biden.
Further south along the Irrawady river, protesters in Pyay wearing hard hats and carrying homemade shields attempted to hold off authorities as they retrieved an injured man.