Authorities in Macedonia were accused of using "dangerous and deplorable" force against migrants protesting at the country's border.
Greece said Maceonian police used tear gas and rubber bullets to push back crowds of people on the border town of Idomeni.
"The indiscriminate use of chemicals, rubber bullets and stun grenades against vulnerable populations, and particularly without reasons for such force, is a dangerous and deplorable act," said George Kyritsis, a spokesman for migration coordinators in the Greek government.
Police sources say they fired only tear gas after migrants stormed towards a border fence on Sunday.
Hundred of migrants and refugees at a makeshift camp on the Greek side of the border stormed the border fence, a Macedonian official told Reuters.
More than 10,000 migrants and refugees have been living at the sprawling tent camp in Greece since February, stranded there after a cascade of border shutdowns throughout the Balkans.
Migrants at Idomeni are demanding that the border with Macedonia be opened, but no migrants have been allowed through for weeks.
Greek authorities have been trying to convince the migrants in Idomeni to move to reception camps, with little success.
More than a million people fleeing conflict poured into Europe mainly through Greece in the past year.
The European Union is implementing an accord under which all new arrivals to Greece will be sent back to Turkey if they don't meet asylum criteria.