Myanmar’s military regime announced Monday that it had executed four pro-democracy activists, the first executions in the Southeast Asian nation in more than three decades and the latest attempt to instill fear in a resistance movement that has continued to battle the junta after it seized power in a coup last year.

The four activists were sentenced to death earlier this year during closed-door trials in a military court without attorneys present. They were executed in secret on Saturday for what the regime called “brutal and inhumane terror acts,” charges that their defenders have said were unfounded.

The executions carried out by the notoriously insular Myanmar military signaled a rebuke to Western leaders, the United Nations and the Association of Southeast Asian Nations, who have all sought to persuade the junta to free political prisoner and halt the violence that has swept the nation since the coup.

Myanmar’s generals have rejected efforts by foreign officials to influence their actions, calling them “reckless and interfering.” And while the regime has mostly ignored attempts at diplomacy, the United Nations Security Council has been unable to introduce harsh sanctions, at least partly reflecting resistance from China and Russia, Myanmar’s allies.

United Nations representatives had urged the junta last month not to proceed with the executions, saying, “These death sentences, handed down by an illegitimate court of an illegitimate junta, are a vile attempt at instilling fear among the people of Myanmar.”

“They do not value human lives and they show that they do not respect the international community,” said U Kyaw Zaw, a spokesman for the National Unity Government, a shadow government established by ousted civilian leaders after the coup. He said the executions were an affront to international efforts by United Nations officials and the Association of Southeast Asian Nations, or ASEAN, to bring peace.

“ASEAN leaders should see the true position of the military by now,” Mr. Kyaw Zaw said. “Killing the activists is outrageous and a sad day for the country.”

All four men who were executed on Saturday — including the popular activist U Kyaw Min Yu, better known as Ko Jimmy, and U Phyo Zeya Thaw, a former hip-hop artist who was elected to Parliament — had been held at the notorious Insein Prison on the outskirts of Yangon, Myanmar’s largest city.

Members of the prison staff confirmed that the executions had taken place and that the four men were executed by hanging. The other two activists executed were U Hla Myo Aung and U Aung Thura Zaw.

Family members, who said they were not notified of the executions, went to the prison Monday morning to confirm that the hangings took place and to try to recover the remains. Relatives had been allowed to speak to the men by video as recently as Friday.

The military, which previously ruled the country for nearly half a century, has faced massive protests and a growing armed rebellion. Since ousting elected officials in the Feb. 1, 2021, coup, the regime has tried to crush dissent by arresting opposition leaders, gunning down unarmed protesters, bombing resistance encampments and burning thousands of homes.

But the regime has been unable to subdue resistance forces, who, along with armed ethnic groups that have been battling the military for years, claim to control about half of the country’s territory.

Among the nearly 12,000 political prisoners being detained by the junta is the ousted civilian leader Daw Aung San Suu Kyi, 77. The Nobel Peace Prize laureate has already been convicted on half a dozen charges and sentenced to 11 years in prison. She faces 13 more counts that carry a maximum cumulative sentence of more than 180 years.

Last month, she was transferred from house arrest to Naypyidaw Prison, where she is being tried in a prison courtroom.

The announcement of the executions drew harsh condemnation from Myanmar opposition leaders, human rights groups and the United Nations special rapporteur on human rights in Myanmar, Thomas Andrews, who urged foreign leaders to take tougher action against the regime.

“My heart goes out to their families, friends and loved ones and indeed all the people in Myanmar who are victims of the junta’s escalating atrocities,” Mr. Andrews said. “These depraved acts must be a turning point for the international community.”

The four men who were executed had a history of opposing Myanmar’s vicious army, known as the Tatmadaw.

Mr. Kyaw Min Yu, 53, was a widely respected democracy activist who rose to prominence during nationwide protests in 1988 as a leader of the 88 Generation Students Group. He spent 15 years in prison for his role in the uprising and another five years in prison for protesting fuel price hikes in 2007.

Mr. Phyo Zeya Thaw, 41, who was known by his stage name, Zayar Thaw, was a member of Generation Wave, a hip-hop collective that challenged the former ruling junta through its lyrics. After spending five years in prison for his activism, he joined the National League for Democracy, the party of Ms. Aung San Suu Kyi, and was elected to Parliament in 2012.

“Hip-hop artists already have a culture of revolution, so in our generation we protested through songs,” he told The New York Times in the weeks after the coup. “Now all kinds of artists are involved because they don’t want to lose the value of democracy.”

Mr. Kyaw Min Yu was arrested in October and Mr. Phyo Zeya Thaw in November. Charged with acts of terror for supporting the armed resistance, they were tried together during a brief trial before a military court without legal representation. They were found guilty in January and sentenced to death. After their appeal was rejected last month, the military’s spokesman, Gen. Zaw Min Tun, defended plans to execute both men.

“At least 50 innocent civilians, excluding security forces, died because of them,” he told a televised news conference. “How can you say this is not justice?”

Zachary Abuza, a professor at the National War College in Washington, said the executions were a desperate move by the junta to show strength, but that it was likely to backfire by turning the men into revolutionary heroes.

“These types of protracted conflicts really need martyrs,” he said. “And in Ko Jimmy and Phyo Zeya Thaw, the junta has created two tailor-made and beloved martyrs that both the international community and domestic population can rally behind.”

Cambodia’s prime minister, Hun Sen, the current chairman of ASEAN, appealed last month in a letter to the junta leader, Senior General Min Aung Hlaing, not to execute Mr. Kyaw Min Yu and Mr. Phyo Zeya Thaw.

The other two democracy activists who were executed on Saturday, Mr. Hla Myo Aung and Mr. Aung Thura Zaw, were arrested in March on charges of killing a woman who had been accused of being an informer. They also were denied attorneys during their brief, closed trial and were found guilty by a military court in April.

Many Facebook users in Myanmar changed their profiles to solid red or black to mourn the executions, including Mr. Phyo Zeya Thaw’s widow, Daw Thazin Nyunt Aung, who wrote, “Must pay back” on her profile page.

Mr. Phyo Zeya Thaw’s mother, Daw Khin Win May, said that when she spoke to her son on Friday, neither had been told he would be executed the next day. On Monday, she said, prison officials refused her request to give his body or ashes to the family.

“I didn’t think my son would be killed so quickly,” she said in an interview. “As a mother, I am proud of my son for giving his life. If possible, I would like to take the ashes and create a monument to the martyrs.”