Pro-democracy activists in Myanmar pledged on Thursday to hold more demonstrations after the UN said 38 people were killed in the most violent day of unrest since last month's military coup. Police and soldiers gave demonstrators little warning before firing live rounds on Wednesday, a day after neighbouring countries called on the junta to show restraint. "We know that we can always get shot and killed with live bullets but there is no meaning to staying alive under the junta so we choose this dangerous road to escape," activist Maung Saungkha told Reuters. "We will fight the junta in any way we can. Our ultimate goal is to remove the junta system from the roots." He said his General Strike Committee of Nationalities group planned to hold a protest against the junta on Thursday. Other activists said that at least two more demonstrations were planned in Yangon, as supporters of elected government leader Aung San Suu Kyi called for her release from detention and recognition of her victory in November elections. Residents said five fighter jets flying in formation made several low passes over the second city of Mandalay early on Thursday, in what appeared to be a show of military might. The UN's special envoy for Myanmar, Christine Schraner Burgener, said that Wednesday was the "bloodiest day" since the February 1 coup after 38 deaths reported. More than 50 people have been killed so far as the military tries to cement its power. Ms Schraner Burgener said the generals who seized power indicated they did not fear renewed sanctions but had been "very surprised" that their plans to restore military rule without much opposition were not working. She said that she told deputy military chief Gen Soe Win that the UN and individual nations "might take huge strong measures" because of the coup. “And the answer was: ‘We are used to sanctions and we survived those sanctions in the past,'” she said. "When I also warned they will go into isolation, the answer was: 'We have to learn to walk with only a few friends.'" A rights group and some media reported different numbers of wounded and dead after Wednesday's violence. Four children were among those killed, an aid agency said. The media reported that hundreds of protesters were arrested. A spokesman for the ruling military council did not respond to requests for comment. Ms Suu Kyi's National League for Democracy party said that flags would fly at half staff at its offices to commemorate the dead. Ms Schraner Burgener said she warned Gen Soe Win that the military would probably face strong measures from some countries and isolation in retaliation for the coup. The UN Security Council is set to discuss the situation on Friday in a closed meeting, diplomats said. UN Special Rapporteur Tom Andrews said the "systematic brutality" of the military was again on display. "I urge members of the UN Security Council to view the photos/videos of the shocking violence being unleashed on peaceful protesters before the meeting," he said. US State Department spokesman Ned Price said the country was appalled by the violence and was considering how to respond. The US told China it was expected to play a constructive role, he said. China declined to condemn the coup, with Chinese state media calling it a "major Cabinet reshuffle". The EU said the shootings of unarmed civilians and medical workers were clear breaches of international law. It also said the military was intensifying its repression of the media, with a growing number of journalists arrested and charged. In Yangon, witnesses said at least eight people were killed on Wednesday, while the media reported six people were killed in the central town of Monywa. "I heard so much continuous firing. I lay down on the ground, they shot a lot," protester Kaung Pyae Sone Tun, 23, told Reuters. Save the Children said four children were killed, including a 14-year-old boy who the US-funded Radio Free Asia reported was shot dead by a soldier on a passing convoy of military vehicles. The soldiers loaded his body on to a lorry and left, the broadcaster reported. Security forces breaking up protests in Yangon detained about 300 protesters, the Myanmar Now news agency reported. Images of a 19-year-old woman one of two shot dead in Mandalay, showed her wearing a T-shirt that bore the message: "Everything will be OK". Video broadcast by Radio Free Asia showed police in Yangon ordering three medics out of an ambulance and beating them with gun butts and batons. Reuters was unable to verify the video independently. The military justified the coup by saying its complaints of voter fraud in the November 8 vote were ignored. Ms Suu Kyi's party won by a landslide, earning a second term. The election commission said the vote was fair. Junta leader Senior General Min Aung Hlaing pledged to hold new elections but gave no timetable. Ms Suu Kyi, 75, has been held incommunicado since the coup but appeared by video at a court hearing this week and appeared to be in good health, a lawyer said.