By Stephanie Nebehay and Karolina Tagaris
GENEVA/LESBOS (Reuters) - The United Nations refugee agency dealt a blow to EU efforts to stem the biggest humanitarian crisis in generations on Tuesday, saying it would no longer assist in the transfer of migrants and refugees arriving in Greece to "detention centers".
The European Union reached a deal with Turkey just four days ago aimed at halting the flow of migrants across the sea to Greece, but the UNHCR said the deal was being prematurely implemented without the required safeguards in place.
It said migrants were being held against their will at reception facilities on several Greek islands, and it would not transport people there from the beaches and to and from ports. It will continue to provide other services including counseling to refugees, it said.
The accord crafted by EU leaders and Turkey specifically mentions the UNHCR's involvement, although UN officials in Geneva said they were not consulted on that.
The deal, which took effect on Sunday, is aimed at putting new arrivals in Greece who seek asylum on a fast track for processing. But it also means those migrants and refugees are kept in detention until their claims are assessed.
"Under the new provisions, these so-called hotspots have now become detention centers," said the UNHCR's Melissa Fleming.
"Accordingly, and in line with UNHCR policy of opposing mandatory detention, we have suspended some of our activities at all closed centers on the island."
Medical charity Medecins Sans Frontieres (MSF) said it was pulling out of one center on the island of Lesbos "because the EU-Turkey deal is turning reception centers to deportation centers.
"If we continued (at the center) we would be participants in a system we deem unfair and inhuman," the Greek MSF branch wrote on Twitter.
Marie Elisabeth Ingres, who heads the charity's mission in Greece, added it would "not allow our assistance to be instrumentalized for a mass expulsion operation."
Those considered ineligible for asylum are to be sent back to Turkey from April 4. For every Syrian returned, another still in Turkey will be resettled directly in Europe, effectively penalizing those who have in many cases spent their life savings trying to flee conflict.
Two EU officials said they hoped this shock therapy might work in ebbing the flow of migrants and refugees into Europe. One said "ugly images" of forced detentions and deportations were something the EU would have to accept if it was to regain control of its own borders.
"Ethically we might have doubts. But legally we have no doubts," another EU official said. Both made the remarks before the UNHCR said it was partially withdrawing its support.
Until Sunday, arrivals to Lesbos had been free to leave the Moria migrant camp and head for ferries to the Greek mainland from where they would mostly head north via the Balkans in a bid to reach western Europe, particularly Germany.
Now, they are meant to be held in Moria or one of four other centers set up on the Aegean islands of Samos, Chios, Leros and Kos, pending the outcome of their asylum applications.
As of Sunday, just two buses were available to transport the arrivals to Moria, one belonging to the coast guard and one to the police, a senior port police official said.
Early on Tuesday, 129 refugees and migrants who had been rescued at sea by a coast guard patrol boat and taken to the port waited for some 40 minutes for the buses to arrive.
They sat on the dock shivering, men dressed in thin trousers and jackets and women wrapped up with scarves. Many were barefoot and soaked to their knees.
One, a young man named Zalmai, said he had left Afghanistan with his five-member family.
"(There are) a lot of problems in our country. We're coming for a better life," he said, putting on a jumper given to him by volunteers and wrapping a thick grey blanket around his waist.
Using his finger to imitate a knife across his throat, he said: "I'm not going back to Turkey, to Afghanistan. Please, I'll stay here."
CHILDREN NEED PROTECTION, UN SAYS
More than 147,000 people, many fleeing conflict in the Middle East and Asia, have arrived in Greece by sea this year, 59 percent of them women and children, according to UNHCR.
On Monday, Turkish monitors arrived on Lesbos to help put the deal into practice. On Tuesday, the Czech Republic offered 10 asylum experts and 30 police officers plus humanitarian aid to Greece, its state secretary for EU affairs said.
Under a timetable agreed with the EU last week, a task force of 4,000 people from asylum case workers and experts to arbitrators, interpreters and security staff should be in place by March 28. Of those, 2,300 should be deployed by other EU states.
A spokeswoman for the U.N. children's fund UNICEF told a briefing in Geneva on Tuesday the fund was concerned about this new agreement and the implications for children.
"We see no mention of children despite the fact that children make up 40 percent of those currently stranded in Greece," she said, adding 19,000 children are stranded in Greece and about 10 percent are unaccompanied.
(Additional reporting by Jan Lopatka in Prague and Stephanie Nebehay in Geneva; Editing by Hugh Lawson and John Stonestreet)