Two Reuters reporters accused of breaking Myanmar's draconian secrecy law during their reporting of a Rohingya massacre must face trial, a judge said Monday, in a ruling swiftly decried as a "black day" for press freedom in the country.

Myanmar nationals Wa Lone, 32, and Kyaw Soe Oo, 28, were arrested in December and accused of possessing leaked sensitive material linked to security operations in crisis-hit Rakhine state.

The pair, who have been held in custody for nearly seven months of pre-trial hearings, were both "charged under the state secrets act", Judge Ye Lwin told the court in Yangon, setting a first court date for July 16.

If convicted the two could face up to 14 years in prison under the colonial-era law.

Reuters says the pair are innocent and were simply doing their job by reporting on a massacre of Rohingya Muslims in September, and has urged the court to dismiss the case.

But Judge Ye Lwin decided the prosecution had shown enough proof that the men were "collecting evidence" from state officials to allow the case to proceed to trial.

The legal action against them has been lambasted by rights groups and foreign observers as an assault on media freedom and an effort to stifle reporting on the Rohingya crisis.

Amnesty International, Human Rights Watch and free speech group Article 19 lambasted Monday's ruling.

"This is a black day for press freedom in Myanmar," said Tirana Hassan, Amnesty International's director of crisis response, labelling the court decision "farcical" and "politically motivated".

Article 19 said the decision underscores Myanmar's "wide-ranging efforts to obstruct reporting on the Rakhine state crisis and to whitewash human rights violations by authorities".

The western state has been largely sealed off from independent monitors since the crackdown started.

During pre-trial hearings the prosecution argued the reporters tried to access "secret papers" about security forces and therefore deserved punishment.

The reporters say they were entrapped by police ─ a version of events seemingly backed up in court by a whistleblowing cop who testified that officers were ordered to set up the reporters.

The pair had been investigating a massacre of 10 Rohingya Muslims at Inn Din village in Rakhine state during last year's military-led crackdown on Rohingya militants.

Before Reuters published its report on the massacre, Myanmar authorities admitted 10 Rohingya men had been extra-judicially killed at the village, later prosecuting several members of the security forces.

But Myanmar has been at pains to say Inn Din was an isolated incident and not part of a wider campaign of ethnic cleansing directed against the Muslim Rohingya, as the United Nations and United States have alleged.

'Deeply disappointed'

Wa Lone, who has issued a defiant "thumbs up" to waiting journalists at each court appearance, vowed to fight the case.

"We have the right to a defence. The court did not decide we are guilty," he said.

In court, Kyaw Soe Oo denied any wrongdoing saying, "I worked as a journalist according to the ethics."

Army operations in August 2017 forced more than 700,000 Rohingya, who are denied citizenship in Myanmar, to flee to Bangladesh.

They took with them harrowing accounts of murder, rape and arson of their villages by Myanmar security forces and mobs of ethnic Rakhine Buddhists.

The European Union, which has sent observers to the Reuters trial in Yangon, renewed calls for the charges against the journalists to be dropped, while the International Commission of Jurists said the prosecution has failed to provided credible evidence of wrongdoing.

In March prominent rights lawyer Amal Clooney, the wife of actor George, joined the Reuters legal team to add weight and profile to their defence.

But the company's efforts were not enough to persuade the judge to dismiss the case.

"We are deeply disappointed that the court declined to end this protracted and baseless proceeding," Reuters Editor-In-Chief Stephen J. Adler said in a statement.