It is the first time Reuters has publicly confirmed what Myanmar nationals Wa Lone, 31, and Kyaw Soe Oo, 27, were working on when they were arrested on December 12 on the outskirts of Yangon.
The pair now face up to 14 years in prison on charges of possessing classified documents in violation of the colonial-era Official Secrets Act.
Their plight has sparked global alarm over withering press freedoms in Myanmar and government efforts to curb reporting in northern Rakhine state – where troops are accused of waging an ethnic cleansing campaign against Rohingya Muslims.
Nearly 700,000 Rohingya have fled the area since last August, carrying stories of atrocities at the hands of troops and vigilante groups in the Buddhist-majority country.
Myanmar authorities deny the allegations but have virtually cut off northern Rakhine, barring independent media from accessing the conflict-hit areas.
On Thursday (Feb 8) Reuters published a report describing how Myanmar troops and Buddhist villagers executed 10 Rohingya men in Rakhine’s Inn Dinn village on September 2, 2017 and dumped their bodies into a mass grave.
“The Reuters investigation of the Inn Din massacre was what prompted Myanmar police authorities to arrest two of the news agency’s reporters,” the report said.
The account was based on testimony from Buddhist villagers, security officers and relatives of the slain men.
It included photographs of the victims, hands bound kneeling on the floor before the killing – and of their bodies in a pit after.
The United Nations said the report’s details were “alarming”.
“This once more attests to the need for a full and thorough investigation by the authorities of all violence in Rakhine State and attacks on the various communities there,” UN spokesman Farhan Haq told reporters in New York.
The US State Department also said the report showed the need for Myanmar to cooperate in an independent probe.
“As with other, previous reports of mass graves, this report highlights the ongoing and urgent need for Burmese authorities to cooperate with an independent, credible investigation into allegations of atrocities in northern Rakhine,” State Department spokeswoman Heather Nauert said.
A month after the journalists’ arrest, Myanmar’s army issued a rare statement admitting that security forces took part in extrajudicial killings of 10 Rohingya “terrorists” in Inn Din village.
The Reuters report said witnesses denied there had been any major attack from Rohingya militants before the alleged massacre.
A Myanmar government spokesman could not be immediately reached for comment.
But Myanmar vehemently denies systematic abuses by its security officers, despite a mounting volume of evidence pointing to atrocities.
Judges have denied bail to the two reporters during a pre-trial hearing period, despite calls for their release from human rights groups and diplomats around the globe.
The next hearing is scheduled for Wednesday (Feb 14).