Three people have been left with stab wounds after rioting broke out on a Greek island amid worsening conditions for refugees.
The UN High Commissioner for Refugees (UNHCR) has called for better safeguards at refugee camps following protests and riots in the "chaotic" and unsanitary environment.
People were particularly injured on the island of Chios, which is reportedly housing 600 more refugees than there is capacity for.
"We are very worried about the situation there. Rioting last night left three people with stab injuries," said the UNHCR on its website.
The humanitarian department also warned that unrest and worry was growing at the Moria facility on Lesvos.
The 2,300 people being kept there is above the camp's stated capacity of 2,000.
"People are sleeping in the open, and food supply is insufficient. Anxiety and frustration is widespread," said the UNHCR.
"Making matters worse, many families have become separated, with family members now scattered across Greece - and presenting an additional worry should returns begin."
Earlier this month, EU leaders finalised a deal aimed at curbing refugee flows across Europe by agreeing that all migrants arriving in Greece across the Aegean Sea would be sent back to Turkey from midnight on Sunday.
One Syrian refugee from camps in Turkey is supposed to be settled for each irregular migrant returned to the country, in a move aimed to discourage asylum seekers from paying huge sums to smugglers for treacherous sea crossings.
Yet the deal has been criticised as contravening international human rights, while aid organisations have said the deal has sparked a "scramble" on the islands with little back-up by authorities.
The UNHCR said: "[We are] urging parties to the recent EU-Turkey agreement on refugees and migrants to ensure all safeguards are in place before any returns begin. This is in light of continued serious gaps in both countries.
"Across Greece, which has been compelled to host people because of closed borders elsewhere in Europe, numerous aspects of the systems for receiving and dealing with people who may need international protection are still either not working or absent."
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