Tran Thi Ngai was 24 and alone at home in her village in Vietnam’s Phu Yen province when a South Korean soldier forced his way into the house and raped her.

“He pulled me inside the room, closed the door and raped me repeatedly. He had a gun on his body and I was terrified,” said Tran, now almost 80, and still waiting for South Korea to acknowledge sexual violence by its soldiers during the Vietnam war.

A campaign group, Justice for Lai Dai Han (JLDH), is urging the country to recognise both the tens of thousands of children born as a result of rape by Korean troops, and their mothers, of whom around 800 are still alive today. Tran’s three children were conceived through rape during the war.

Roughly 320,000 South Korean soldiers were deployed to Vietnam to fight alongside the US between 1964 and 1973, but the story of the country’s involvement in the conflict is largely untold. South Korea has never acknowledged claims of sexual violence allegedly perpetrated by its troops against thousands of women and girls, some as young as 12 – or the children born as a result.

However, South Korea has continued to demand apologies from Japan for its use of “comfort women” from Korea, who were forced to work in Japanese military brothels before and during the second world war.

This week, at an event to highlight work to prevent sexual violence in conflict, former British foreign secretary Jack Straw called on the UN human rights council to conduct a full investigation into sexual violence during the Vietnam war, and urged South Korea to confront a murky period in its past.

“Facing up to unacceptable behaviour by troops is difficult for any country. However, as we have learned in the UK through painful experiences like Bloody Sunday, uncovering the truth not only gives victims and their families closure but can strengthen a nation and its values,” said Straw, who is an international ambassador for JLDH.

Korean troops guard three Vietnamese captives found near a village south of Tuy Hoa in November 1966. Photograph: Hong/AP

“The victims of sexual violence and the Lai Dai Han deserve recognition and an opportunity to heal. We must demonstrate to the world the importance of following through on commitments to end sexual violence in conflict.”

“Lai Dai Han” is a pejorative term meaning “mixed blood” in Vietnamese. The Vietnamese-Korean children say their lives have been blighted by stigma in a society that has acknowledged neither them nor the sexual violence suffered by their mothers. Many are illiterate because they were refused an education, and they have poor access to healthcare and social services.

Tran Dai Nhat, the son of Tran Thi Ngai, recalled being beaten by teachers and thrown out of school when he was a child. It was not until he was 18 that his mother finally explained the discrimination was because he was mixed race.

“At school they said I was the son of a ‘dog’. I couldn’t do anything and I never understood why,” he said. “Teachers hit me – saying I should go back to Korea with my father. My entire life, I have been made to feel as though I shouldn’t be [in Vietnam],” said Tran Dai Nhat, who founded JLDH and leads efforts to press for recognition and an apology from South Korea.

Nadia Murad, who won last year’s Nobel peace prize with Congolese doctor Denis Mukwege for their work to stop the use of sexual violence as a weapon of war, backed JLDH’s calls for recognition, saying: “The Lai Dai Han have been living in the shadows of Vietnamese society for far too long. The victims and their families deserve to be recognised as we work together to achieve justice.”

Murad, who was forced into sexual slavery by Isis militants with other Yazidi women in Iraq, said more needed to be done to bring perpetrators of sexual violence to justice. “As these criminals enjoy more rights, freedom and life than the victims themselves, how can we restore dignity to the victims if everyone turns a blind eye to the prosecution of perpetrators and allows them to enjoy impunity?”

Former British foreign secretaries Jack Straw and William Hague with 2018 Nobel laureate Nadia Murad and Tran Thi Ngai, whose son is seen on the far right. Photograph: Courtesy JDHL

William Hague, co-founder of the Preventing Sexual Violence Initiative, said the case of the Vietnamese families showed the importance of confronting the past in order to move forward on preventing sexual violence in war. “There is now an overwhelming case for a permanent investigating body, under the auspices of the UN, to help ensure these atrocities can be prevented and justice made available,” he said.

Straw told the Guardian: “This is not about compensation. Above anything, what these families want is recognition.”

Straw added that he is pressing South Korea to apologise to families affected by sexual violence during the Vietnam war.

But Tran Thi Ngai accepts that such an apology may be far off. “I lost everything after I was raped. I was imprisoned, I lost my home and my children lost their future. Any apology will probably come when I am dead. But I will accept it, even in the afterlife.”