Two Reuters journalists in Myanmar accused of breaking a state secrets law while investigating a massacre of Rohingya Muslims face another week of uncertainty after the verdict in their trial was delayed on Monday.

Wa Lone, 32, and Kyaw Soe Oo, 28, have been detained in Myanmar's infamous Insein prison since December in a case which has sparked a global outcry.

The reporters had been investigating the September 2017 killing of 10 Rohingya Muslims in conflict-scarred Rakhine state, a week after Myanmar's military launched a sweeping crackdown on members of the stateless Muslim minority.

They were invited to dinner with police in Yangon, handed some documents, and then arrested as they left the meeting and accused of possessing classified material on operations in the area.

The pair were charged with violating the state secrets act, which carries a maximum sentence of 14 years.

Timeline: Reuters journalists detained in Myanmar

The expected ruling at the court in northern Yangon had drawn a crowd of diplomats, well-wishers and media, some wearing t-shirts with the words "Journalism is not a crime".

But district judge Khin Maung Maung said the presiding judge was ill and the verdict would be announced on September 3.

Wa Lone told reporters as he left the courthouse that they were not afraid, whatever the decision.

"We have the truth with us and we did not do anything wrong," he said.

Suu Kyi under fire

The case has sparked fears of eroding press freedoms under civilian leader Aung San Suu Kyi, whose international reputation has been tarnished by the treatment of the Rohingya.

Defence lawyer Khin Maung Zaw said the delay could be linked to global developments on Myanmar.

A UN fact-finding mission on rights abuses in the country released a report on Monday, in which investigators said that top Myanmar military leaders should be prosecuted for genocide against Rohingya Muslims. The UN Security Council will discuss the Rohingya crisis on Tuesday.

"If the verdict is today and it’s negative for the defence, it may be seen as a negative approach to democracy," he said.

Reuters has robustly denied the charges. The defence has said the supposedly secret documents had already been published, and the prosecution case hit a hurdle when a police witness said his superior had ordered his men to entrap the pair.

The company said after the court announcement that it was disappointed.

“Wa Lone and Kyaw Soe Oo have already spent more than eight months in prison based on allegations of a crime they did not commit," a statement said.

"We look forward to receiving the verdict next week, when we very much hope that they will be acquitted and reunited with their families."

The journalists have described in detail what happened after their arrest, saying they were hooded and deprived of sleep in initial interrogations, which included questions about their work on Rakhine.

The news agency launched a worldwide advocacy campaign that included diplomats, celebrities and the legal assistance of prominent rights attorney Amal Clooney.

But it was not enough to keep the court in the Buddhist-majority country from pursuing the charges.

The United Nations and Washington have called the military campaign "ethnic cleansing", after some 700,000 Rohingya fled Rakhine to Bangladesh, bringing with them testimonies of rape, arson and killings in the northern part of the state.

Myanmar rejects the charges. But it has admitted that the killing of 10 men and boys investigated by Reuters in the village of Inn Din took place and sentenced seven soldiers for the crime.

Rights groups say security forces should be investigated for crimes against humanity in Rakhine, but so far only a handful of targeted sanctions have hit figures in Myanmar's armed forces.