Four democracy activists have been executed by Myanmar's military in what is believed to be the first use of capital punishment in decades.

The four - including activist Ko Jimmy and lawmaker Phyo Zeya Thaw - were accused of committing "terror acts".

They were sentenced to death in a closed-door trial that rights groups criticised as being unjust.

Family members of the deceased gathered at Insein prison on Monday desperate for information on their loved ones.

The mother of Zayar Thaw says she was not told when exactly her son would be executed, adding that she was unable to make proper traditional funeral plans as a result.

"When we met on Zoom last Friday, my son was healthy and smiling. He asked me to send his reading glasses, dictionary and some money to use in prison, so I brought those things to the prison today," Khin Win Tint told the BBC's Burmese Service. "That's why I didn't think they would kill him. I didn't believe it."

Meanwhile, the sister of Ko Jimmy - whose real name is Kyaw Min Yu - had earlier said they were yet to receive the bodies.

The families have all submitted applications for information on the executions.

State news outlet Global News Light of Myanmar said the four men were executed because they "gave directives, made arrangements and committed conspiracies for brutal and inhumane terror acts".

It said they had been charged under the counter terrorism laws, but did not say when or how they were executed.

The executions are the first since 1988, according to the United Nations. Previous executions in Myanmar have been by hanging.

In 2021, the country's military seized power, an event which triggered widespread demonstrations, prompting a military crackdown on pro-democracy protesters, activists and journalists.

News of the killing was met with intense criticism from opposition groups and human rights organizations.

"I am outraged and devastated at the news of the junta's execution of Myanmar patriots and champions of human rights and democracy," said UN Special Rapporteur on Human Rights in Myanmar Tom Andrews. "These depraved acts must be a turning point for the international community."

The shadow National Unity Government of Myanmar (NUG) said they were "extremely shocked and saddened" by the killings.

The NUG - a group which comprises pro-democracy figures, representatives of armed ethnic groups and former lawmakers that was formed in response to the 2021 military coup - urged the international community to "punish (the) murderous military junta for their cruelty and killings".

Ko Jimmy, 53, was a veteran of the 88 Generation Students Group - a Burmese pro-democracy movement known for their activism against the country's military junta in the 1988 student uprisings.

He, alongside his wife, fellow activist Nilar Thein, were considered some of the pioneers of the pro-democracy movement.

When monks led protests against the regime in 2007, Ko Jimmy and his wife mobilised activists and protesters from the 1988 demonstrations to participate.

He served multiple stints in prison for his activism, before being released in 2012.

He was arrested in October last year after being accused of hiding weapons and ammunition at an apartment in Yangon and being an "advisor" to the National Unity Government.

Phyo Zeya Thaw, 41, was a former hip-hop star turned NLD lawmaker.

His band Acid released Myanmar's first ever hip-hop album, with his lyrics carrying thinly-veiled attacks on the military drawing the ire of the junta.

He gradually became a close ally of pro-democracy icon Aung San Suu Kyi, and often accompanied her on her international meetings with world leaders.

He was arrested in November for alleged anti-terror offences.

Both Phyo Zeya Thaw and Ko Jimmy lost their appeals against their sentences in June.

Less is known about the two other activists - Hla Myo Aung and Aung Thura Zaw. They were sentenced to death for killing a woman who was an alleged informer for the junta.

The military has claimed the results of a general election that saw Suu Kyi's political party winning by a landslide were rigged - an accusation election commission officials denied, saying there was no evidence of fraud.

Since the coup, Suu Kyi has been detained under house arrest, and slapped with a litany of charges ranging from corruption to violating the country's official secrets act, which could see her serving a sentence of up to 150 years.

The Assistance Association for Political Prisoners (AAPP), which keeps a toll of those killed, jailed or detained by the military, says that 14,847 people have been arrested since the coup, with an estimated 2114 having been killed by military forces.