TOKYO - Japan is not at fault for the inability of parents to see their children after separating despite having visitation rights, a court ruled on Friday, in a case that critics say highlights the ineptitude of a judicial system that lacks enforcement powers.

Fourteen parents had sued the government claiming damages of 9 million yen ($82,900), arguing that having no legal framework to ensure proper access to children was unconstitutional.

Parental alienation has long been an acute problem in Japan, with children often losing contact with the non-custodial parent after an acrimonious split.

Unlike most developed countries, Japan has no joint-custody system after divorce, and court-ordered visitation rights are often ignored with impunity.

The World Health Organisation this year classified parental alienation as a health condition, while the United Nations stipulates children should have the right to maintain bonds with both parents.

In the Tokyo District Court ruling, presiding judge Tatsuro Maezawa said the UN treaty was "merely an agreement to respect" those rights but had no binding power.

Tommaso Perina, an Italian resident of Tokyo and the only non-Japanese plaintiff, said the ruling went against the Supreme Court's stance, expressed in a parliamentary committee last week, that judges must adhere to international treaties in handing out rulings.

Perina lost custody of his children after his wife decided unilaterally in late 2016 not to return to Tokyo from her hometown to the north. Perina said he has not seen his children, aged 6 and 4, for more than two years.

A family court rejected Perina's plea for custody and granted him two hours' visitation a month.

Court documents reviewed by Reuters show Perina's wife had claimed domestic violence but the judge ruled against her, saying her testimony lacked credibility.

"It's ridiculous – you'd spend more time with a pet turtle," Perina told Reuters. "But my wife is refusing even that. I'm worried about my children because Japanese courts don't seem to understand what's in the best interest of children."

Multiple attempts by Reuters to reach Perina's wife by telephone were unsuccessful.

Perina remains married to her, has full parental rights and has been paying alimony of 170,000 yen a month since December 2016.

Perina has sought help through diplomatic channels - Ambassador Giorgio Starace called his situation a case of "minor abduction" - while even Prime Minister Giuseppe Conte spoke to his Japanese counterpart, Shinzo Abe, to no avail.

"I've reached the peak of what I can do," Perina said.

"Because when you have the head of a state talking for your kids and they cannot help the situation... Who can ask for more than that?"