The UN's highest court on Wednesday narrowly threw out landmark cases brought by the tiny Marshall Islands against India, Pakistan and Britain for allegedly failing to halt the nuclear arms race.

In majority and sharply divided decisions, a 16-judge bench at the International Court of Justice (ICJ) ruled there was no evidence that Majuro had a prior dispute with any of the three nuclear giants or had sought negotiations on the issue.

"The court upholds the objection to jurisdiction" raised by each of the countries, presiding judge Ronny Abraham said in separate rulings, and therefore the tribunal "cannot proceed to the merits of the case."

The tiny Pacific island nation, with a population of 55,000, was ground zero for a string of devastating nuclear tests on its pristine atolls between 1946-58, carried out by the United States as the Cold War arms race gathered pace.

After the hearings, the Marshalls said it will now "study the ruling" which is final and without appeal.

"Obviously it's very disappointing," Marshall Islands lawyer Phon van den Biesen told reporters.

"It's a dispute that is clear to all of the world except for the judges here," he said, outside the courtroom in the ICJ's historic headquarters in the Peace Palace in The Hague.

- 'Sky turned blood-red' -

Initially in 2014, Majuro had accused nine countries of failing to comply with the 1968 nuclear Non-Proliferation Treaty (NPT), which seeks to inhibit the spread of atomic bombs.

But the ICJ already refused to take up cases against the other countries -- China, France, Israel, North Korea, Russia and the United States -- as they have not recognised the court's jurisdiction.

Israel has also never formally admitted to having nuclear weapons.

The Marshall Islands argued that by not stopping the nuclear arms race Britain, India and Pakistan had breached obligations under the treaty -- even if New Delhi and Islamabad have not signed it.

At a poignant March hearing, Majuro's lawyers painted a vivid picture of the horrors caused by 67 nuclear tests notably the atolls of Bikini and Enewetak.

"Several islands in my country were vaporised and others are estimated to remain uninhabitable for thousands of years," Tony deBrum, a former Marshall Islands foreign minister, told the court.

"The entire sky turned blood-red," said deBrum, who was nine when he witnessed the blasts.

Judge Abraham noted the archipelago, "by virtue of the suffering which its people endured as a result of it being used as a site for extensive nuclear testing, has special reasons for concern about nuclear disarmament."

"But that fact does not remove the need to establish that the conditions for the court's jurisdiction are met," Abraham said.

- 'Horrific weapons' -

The so-called "Operation Castle" tests in March and April 1954 were particularly devastating and resulted in massive contamination due to nuclear fall-out.

The NPT commits all nuclear weapon states "to pursue negotiations in good faith on effective measures relating to cessation of the nuclear arms race at an early date."

Critics had argued however that the ICJ action was a distraction as the islanders' real fight was with Washington.

They contended the case was unrelated to the victims' claims for increased compensation, better health care and clean-ups to render the sites habitable again.

The islands hoped however to reignite the debate over the disarmament talks, which have stalled over the past two decades.

"The Marshall Islands decided to bring these cases because they come from a notion that in the end nuclear weapons are the most horrific weapons on earth," said Majuro's lawyer Van den Biesen.

Experts told AFP there had always been a possibility the case could "backfire".

"That it happened this early is certainly very disappointing for them and the whole nuclear disarmament movement," said Joris Larik, senior researcher at The Hague Institute for Global Justice

"But it also shows that small island nations are looking for smart ways to play a role on the global stage. Sometimes they succeed and in a case like this, perhaps not so much."