Nearly 50,000 people stuck in Greece under miserable conditions are at risk of being "forgotten" while the world's attention is fixed on the EU-Turkey deal, Amnesty International warned Monday.
The migrants and refugees became stranded in Greece when countries to the north, starting with Macedonia, closed their borders last month, preventing passage towards wealthy EU countries, most of all Germany.
"The decision to close the Western Balkans route has left more than 46,000 refugees and migrants in appalling conditions and in a state of constant fear and uncertainty," said John Dalhuisen of Amnesty International, an international human rights watchdog.
The European Union agreed with Turkey to return or resettle all migrants and refugees arriving on Greek islands after March 20, but the processing of their asylum claims is painfully slow, leaving many stranded.
Of the 66,400 asylum seekers pledged to be relocated from Greece in September 2015, only 615 had been transferred to other EU member states by April 12, Amnesty said in a report released Monday, quoting European Commission figures.
The slow process raises the prospect of a humanitarian crisis due to inadequate conditions in many of the accommodation sites in Greece, Amnesty said.
The organization called for Greece to improve its asylum system and ensure access to protection for everyone trapped on its soil.
It also called on EU member states to accept asylum seekers from Greece through the existing emergency relocation scheme.
Meanwhile, Greece returned a first group of migrants to Turkey in two weeks, Greek station Radio 984 reported.
Forty-five Pakistanis boarded a Turkish ship in Lesbos that was to take them to the Turkish port of Dikili, with a total of 150 people due to be returned during the day, according to the station.
Greece can return people only after it processes their claims for asylum, which has led to a bottleneck - only 300 have been sent back since the returns started April 4 - amid a severe personnel shortage.
Greek Deputy Defence Minister Dimitris Vitsas said over the weekend that only around half of the 2,300 asylum experts that Athens requested for the implementation of the agreement have started work.