Greece is pressing ahead with plans to start deporting migrants and refugees back to Turkey next week, despite mounting concern from the UN and human rights organisations that Syrians could be denied proper protection.
Parliamentarians in Athens are due to back fast-tracked draft legislation to allow the returns to begin as soon as Monday.
The operation would see migrants and refugees who arrived on Greek islands after March 20 put on boats and sent back to Turkey.
Greek officials said deportations are likely to start from the island of Lesbos, with migrants from Afghanistan, Pakistan and other countries whose asylum claims are considered inadmissible.
The transport is set to be carried out under heavy security escort - with one police minder for every migrant - using buses that will travel from island detention camps and are likely to board straight onto chartered vessels.
The imminent deportations, which are backed by the European Union following its recent agreement with Turkey, have triggered more violence at detention camps in Greece.
Authorities on the Greek island of Chios said several hundred people broke out of an overcrowded detention camp and headed to the island's main town on foot, following overnight clashes between Syrian and Afghan detainees that left five people injured.
The clashes are the latest in a series of violent incidents at shelters and gathering points across Greece, where more than 50,000 migrants and refugees are stranded following Balkan border closures supported by the EU.
More than 10,000 of those stranded remain camped out at the Greek-Macedonian border, ignoring calls by the government to move voluntarily to organised shelters.
In Geneva, Switzerland, the UN refugee agency, or UNHCR, urged Greece and Turkey to provide further safeguards for asylum seekers before the returns begin, noting that conditions are worsening by the day for more than 4,000 people being held in detention on Greek islands.
Amnesty International, which has strongly opposed the EU-Turkey agreement from the start, said it has evidence of Turkish authorities rounding up Syrians and sending them back across the border to their conflict-torn country.
The group said Turkey has been expelling around 100 men, women and children on an almost daily basis since mid-January.
Amnesty's Europe and Central Asia director John Dalhuisen said: "EU leaders have wilfully ignored the simplest of facts: Turkey is not a safe country for Syrian refugees."
Greek officials did not respond to the criticism directly, but insisted the rights of detained asylum seekers are being protected.
Migration affairs minister Ioannis Mouzalas told the Greek parliament: "I assure you that we will strictly observe human rights procedures, not what people are inventing, but what is required under the circumstances.
"I was yesterday in Geneva yesterday, and the UNHCR tweeted positive things about our country."