(CNN) For months, Mai Linh prayed.
She prayed for justice for her only son Quan when he was held on drug charges in a maximum-security prison in Vietnam. She prayed for his physical health and mental well-being, that he would be looked after in prison because she could no longer see him due to heightened Covid-19 restrictions.
And most of all, she prayed for his safe return.
Quan, a salesman, was found guilty of drug trafficking and sentenced to death by lethal injection. He was executed in 2021 at the age of 31.
Strapped flat on his back in a straightjacket, he was tied to a gurney and injected with a cocktail of deadly drugs. But unlike in other countries such as the United States that use lethal injections in states like Texas, Mai Linh wasn't permitted to be with her son during his final moments.
"There is nothing, nothing, that can prepare you for something like that," Mai Linh said. "There isn't a day that goes by when I don't think about how he died. The pain is unexplainable."
"The death penalty is a different kind of evil," she added. "One that will haunt me for the rest of my life."
Vietnam is famously secretive about its use of capital punishment. However, rights groups believe it to be one of the biggest executioners in the world and the biggest in Southeast Asia. Previously classified government data made public and published in Vietnamese state media outlets in 2017 revealed 429 executions had taken place between 2013 and 2016 -- putting the country behind only China and Iran in its use of the death penalty.
A report released by Amnesty International this week found that global executions had risen by 20% as Covid-19 restrictions in countries eased. However, as in previous years, it did not include China and Vietnam where executions are regarded are state secrets. But Amnesty could confirm "partial disclosures" by Vietnamese authorities that indicated a rapid increase in the number of death sentences by nearly 30% -- which were handed out between October 1, 2020 and July 31, 2021. It also said that 11 execution centers across the country had been "put to use" throughout the year.
The group now believes there to be more than 1,000 people on death row in the country -- among them foreigners from Laos, Cambodia, Singapore and Malaysia and a 73-year-old Australian woman convicted of drug trafficking.
The ruling Vietnamese Communist Party has long defended and justified its use of the death penalty. State documents released in 2017 showed approvals for lethal injections by the public security ministry.
CNN reached out to the Vietnamese government for comment on this story but received no response.
Vietnam remains the biggest executioner in Southeast Asia, suggested by figures in Amnesty's report although the situation in Myanmar also got a mention.
"An alarming increase in the number of known death sentences was recorded in Myanmar, where the death penalty became a tool for the military in the ongoing and widespread persecution, intimidation and harassment of and violence on protesters and journalists," the report said.
While no executions took place in Myanmar in 2021, at least 86 recorded death sentences were meted out -- up from previous years, when the number of death sentences remained fewer than 10. Among them were 65 people sentenced to death by military tribunals.
Disturbing pictures published earlier this year also appeared to show prison gallows being prepared for what rights groups say would be the first official executions in the country for over three decades.
Under martial law regulations, junta chief Min Aung Hlaing approves all executions and has the authority to overturn executions or commute death sentences to lesser penalties. There is "no appeal for decisions or convictions handed down" by a military tribunal, according to junta officials.
CNN reached out to junta officials for comment on this story but received no response.
No executions were recorded in 2021 in neighboring Singapore and Indonesia, both of which carry out death sentences for murder, possession of firearms and drug trafficking, though Singapore resumed executions in 2022. The city state executed Malaysian citizen Nagaenthran K Dharmalingam -- an intellectually disabled man found guilty of drug trafficking -- in April.
"Data on the death penalty in Vietnam continues to be classified as a state secret," said Amnesty's death penalty expert Chiara Sangiorgio.
"[This] secrecy and the fact that media in the country are tightly overseen or controlled by the state has certainly contributed to a lack of information and international spotlight on the subject.
"We have written to the authorities seeking information, as we do for all countries that still retain the death penalty every year in preparation of our report. We did not receive any response."
The vast majority of Vietnamese death sentences are related to drug offenses, which according to Amnesty accounted for 93 out of the 119 death sentences handed down last year.
Others awaiting execution include once-powerful businessmen convicted of corruption, embezzlement and fraud. Nguyen Xuan Son, a former high-flying official who once served as the head of a major Vietnamese bank, was sentenced to death in 2017 for his role in a fraud involving millions of dollars in illegal loans. Others, too, have been convicted on state corruption charges.
Others on death row have been convicted of murder.
Last year, a court in the capital, Hanoi, upheld the death sentences of two brothers, Le Dinh Cong and Le Dinh Chuc, both farmers, for their roles in the killings of three police officers who were burned to death during violent clashes in their village.
Villagers blamed the violence on authorities' attempts to build a wall on farm land. Judges defended the death sentences, saying the brothers had ignored the law and "showed no respect" for the lives of security personnel.
Vietnam's suspected rise to top executioner in Southeast Asia may come as a surprise to some but rights groups warn that executions in the country are likely to increase in the years to come.
"Vietnam continues to execute people at an astonishing rate," said Ben Swanton, advocacy director of the 88 Project, a non-profit organization advocating for free speech and human rights in the country.
"The Vietnamese Communist Party is aware that its use of the death penalty contradicts its narrative of the country being a peaceful and harmonious society and has the potential to damage its international reputation."
Human Rights Watch's Asia deputy director Phil Robertson called Vietnam "one of the worst rights-abusing states" in Southeast Asia.
"The death penalty in Vietnam is used to intimidate those who would break the law, while also showing the power of the ruling party," Robertson said. "This is a government that chases down dissidents, runs roughshod over civil society, sentences and imprisons people after kangaroo court trials, and now we know, executes far more people than anyone else in [the region]."
Comparing it to neighboring Singapore and Indonesia, countries that have made bigger headlines over the years with their execution cases, Robertson said: "Vietnam's horrendous record of executions dwarfs that of any of its neighbors but it is not surprising that the government has systematically implemented the death penalty and kept executions out of the public eye."