Sam Serey, president of the Khmer National Liberation Front (KLNF), is, according to Cambodia’s courts, the ringleader of an international organization that planned to topple the government of Prime Minister Hun Sen.

Along with 12 associates, Mr. Serey was sentenced to prison by the Phnom Penh Municipal Court on Friday over the alleged terrorist plot.

Seven of the group’s members, who were present in court, are set to spend the next five to seven years of their lives in jail.

But Mr. Serey, who was among six KNLF members tried in absentia, is living in Denmark, where he claims to have been granted political asylum in 2010.

When he is not drafting screeds against the impunity and corruption within Mr. Hun Sen’s government, Mr. Serey says he volunteers for the International Red Cross in Denmark and is studying the Danish language at VIA University College in Aarhus.

“I think the verdict is very injustice for us because we are working peacefully to find justice, freedom and democracy for Cam­bodia,” Mr. Serey said on Sunday, speaking by telephone.

While living from 2005 to 2010 among the Cambodian population in Thailand’s Pathum Thani prov­ince—where six KNLF members were arrested by Thai police last year and returned to Cambodia—Mr. Serey says he built a network of like-minded dissidents.  He launched the KNLF from Denmark in December 2012.

“There are more than 5,000 members, they just distribute leaflets and books to tell Cambodians what is happening in Cambodia,” Mr. Serey said.

“We have no intention to use violence against this regime.”

With seven KNLF members sentenced to spend more than half a decade in prison, Mr. Serey said he would seek help from foreign organizations and embassies to push for their release.

“I have to do anything to be responsible for their release. I am gong to find help from the international community to put pressure for their release,” Mr. Serey said, adding that his members would appeal the municipal court’s decision.

“I am not sure when but they will,” he said.

In the months before July’s national election, Prime Minister Hun Sen said that the KNLF was among at least three terrorist groups with ties to the opposition CNRP. Human Rights Watch said last week that the arrest and imprisonment of KNLF members was purely politically motivated.

Mr. Serey said that his group has no formal ties to the opposition party, but added: “Many members of CNRP support the KNLF.”

“Our group is the true democrats and we would do anything to help the Cambodian people to have freedom and democracy,” he said.

But Mr. Serey said he would continue his fight for democracy in Cambodia from the outside.

“If the country has the real democratic system I will be back to Cambodia, but not yet,” he said.