Migrants clashed with Macedonian police on April 10 after they were stopped from scaling a border fence between Macedonia and Greece.
Reports said police used tear gas, stun grenades, and rubber bullets to push back the migrants, who responded by throwing rocks at the officers.
Aid organization Doctors Without Borders said its medical volunteers on site treated some 300 people for breathing problems from the gas, cuts, bruises, and impact injuries from plastic bullets. At least six injured were hospitalized.
Macedonian police said 23 members of the security forces were injured, including five seriously.
The violence occurred near the Idomeni crossing, where more than 11,000 migrants are camped out on the Greek side of the border.
Balkan states closed off the migrant route to northern Europe in mid-February.
The unrest reportedly began after a crowd of 500 people reacted to rumors that the border was about to open.
After the rumor was denied by the Macedonian police, more than a hundred migrants, including children, tried to climb the fence twice but were pushed back as the clashes continued into the afternoon.
The wind brought tear gas fumes into the Idomeni camp where people not involved in the clashes suffered from respiratory problems.
Greek policemen stood by without intervening.
George Kyritsis, a spokesman for migration coordinators in the Greek government, said the use of force by Macedonian police was a "dangerous and deplorable act."
Greek authorities estimate that there are around 53,000 migrants stranded in the country.
Under the EU-Turkey deal, all new migrants crossing from Turkey into Greece from March 20 will be returned to Turkey.
For every Syrian being returned to Turkey from Greece, a Syrian refugee will be resettled from Turkey to the EU.
The agreement has been condemned by rights groups.