In one of its firmest statements yet, the 28-nation bloc, which is a significant donor to Myanmar, said that the case of Wa Lone and Kyaw Soe Oo was an important test for the country's commitment to developing democracy after years of military rule.
"It's not as though there are human remains lying around everywhere", said John Sifton, Asia advocacy director at Human Rights Watch. "We have talked with the defendants and the statements of defendants differ from the submitted evidence".
Human rights groups have accused the police of entrapping the two Reuters journalists by giving them documents that were then deemed state secrets.
Prosecutors in Myanmar formally charged two journalists from the Reuters news agency on Wednesday with violating the Official Secrets Act, signalling the case will go forward despite worldwide condemnation.
In its account of the Inn Din massacre the army chief's office said security forces captured 10 Rohingya militants before killing them as violence engulfed the village and its surrounding area. The military responded with what it called "clearance operations".
"ARSA has.no other option but to combat "Burmese state-sponsored terrorism" against the Rohingya population for the objective of defending, salvaging and protecting the Rohingya community", the group said in a statement signed by leader Ata Ullah and posted on Twitter.
The two men allegedly obtained documents illegally from officials in Rakhine state, where the Myanmar military has been conducting operations that have been described as "ethnic cleansing" - by both the US and United Nations - against the country's Rohingya Muslim minority.
"The court rejected the petition and has upheld the administrative order, which bans marriage between Bangladeshi citizens and Rohingya people", deputy attorney general Motaher Hossain Saju said. "This incident happened because ethnic Buddhist villagers were threatened and provoked by the terrorists". They are widely called "Bengalis" and are accused of migrating illegally from Bangladesh.
Though limited in scope, Wednesday's message appears to contradict previous denials that Myanmar's military was involved in violence.
The U.N. and other groups accuse the military of widespread atrocities against Rohingya, including killings, rapes and the burning of homes. The Myanmar government has consistently denied all accusations.
The circumstances have elicited protests the government set them up - and, as The New York Times reports, Wa Lone's wife says he never even had the opportunity to read the documents before being detained.
"It was found that there were no conditions to transfer the 10 Bengali terrorists to the police station and so it was made a decision to kill them", it said.
"This grisly admission is a sharp departure from the army's policy of blanket denial of any wrongdoing". "That is precisely why you need worldwide observers and investigators involved now", he added.
See more from the BBC here and Washington Post here.