BANGKOK (AFP) - Buddhist monks opened an emotionally charged commemoration Thursday (Oct 6) on the 40th anniversary of a massacre of student protesters in Bangkok, as survivors reflected on a battle for democracy that appears lost in junta-run Thailand.

The killings of October 6, 1976 marked a nadir in the kingdom's blood-splattered recent history.

At least 46 student protesters were shot, beaten to death or hung from trees as they massed at Thammasat University against the return from forced exile of hated military dictator Thanom Kittikachorn.

Survivors say the true toll was at least twice as high, with thousands more arrested or forced into hiding.

Fearing a leftist rebellion in a region where many countries had turned communist, security forces - flanked by royalist armed militias - ruthlessly cracked down on the students.

No state apology has ever been issued and no officials have been held to account for the deaths - a reflection, critics say, of a culture of impunity for the military that endures to this day.

At dawn on Thursday survivors gathered under heavy drizzle around a permanent memorial at the university's entrance where the assault began.

Some held candles, others wore T-shirts with the slogan "I think therefore I am dead" featuring a hanged man - a reference to the lynching of students who were strung from trees near the campus.

"There were many killed and injured on that day," Sinsawat Yodbangtoey, 63, who was an art student at a nearby college when he joined the Thammasat protests.

"Even though I wasn't injured... my heart is wounded." The October 6 crackdown ended a brief three-year flirtation with democracy and ushered in another 16 years of military-led rule.

Thailand is once again under military rule, with the kingdom's democracy movement hemmed in by repressive laws.

The last coup in 2014 - the army's twelfth successful power grab since 1932 - came four years after soldiers once more opened fire on pro-democracy protesters on Bangkok's streets.

Many newspapers nonetheless used the rare space provided by Thursday's anniversary to recall dark chapters from the military's past, while graphic photos of student hangings were widely shared on Thai social media.

Sirawith Seritiwat, a 24-year-old Thammasat student and one of a handful of activists protesting against the current junta, said remembering the past is vital in a country with a proclivity for collective amnesia over difficult events.

"There was an effort by many people, (Thai) governments and leaders, to forget history," he told AFP.

"They want reality to be hidden." Thailand military says its partnership with the monarchy is the only way to ensure stability in a politically fraught country.

The royal palace's role in the tragic events of October 1976 remains under-explored - partly because Thailand's strict royal defamation law makes such discussion impossible.

In a rare interview aired in 1979 King Bhumibol denied "playing politics" with the Thammasat protests which resulted in a coup he later validated.

Four decades on, survivors are determined to remember their fallen friends.

Prommin Lertsuridej, 62, who fled to the jungle for four years to avoid arrest after the protest, said October 6 was a "hugely important" moment in modern Thai history.

"We gather every year to show we were not people who destroyed the country - but we are the ones who want to create fair society," he added.