By Tulay Karadeniz and Noah Barkin
ANKARA/BERLIN (Reuters) - German Chancellor Angela Merkel will try to soothe tensions over a deal meant to stem the flow of migrants to Europe when she visits Turkey this weekend.
The pact, which came into force three weeks ago, aims to help end the chaotic arrival of migrants and refugees on the Greek islands, many fleeing war and poverty in the Middle East and Africa. More than one million reached Europe last year.
The deal initially slowed the number of arrivals to Greece sharply, but boats have been coming again with about 150 people a day, the International Organization for Migration said.
Merkel and European Council President Donald Tusk will go to Gaziantep near the Syrian border on Saturday, where they are due to visit a refugee camp and meet Prime Minister Ahmet Davutoglu.
There is much at stake for both sides. Merkel lobbied skeptical European partners to back the deal, under which Turkey agreed to take back migrants who cross the Aegean Sea illegally, and is under political pressure at home to show progress.
Davutoglu sold the deal to the Turkish public partly on the basis that Turks would win quicker visa-free travel to Europe in return, a pledge that now could go unfulfilled, at least by the June deadline he had wanted.
"Turkey wants support in easing the refugee burden - both financial support and in terms of numbers. And they want visa liberalization. We have other interests," a Merkel aide said.
"Ultimately it will depend on both sides fulfilling the criteria they need to. If that doesn't happen the deal won't work."
Rights groups have questioned the legality of the deal, which hinges on Turkey being a safe country of asylum. Amnesty International says Turkey has illegally returned Syrians to their war-torn homeland, a charge Ankara denies.
Under the deal, Ankara gets more EU funding for refugees living on its soil and the revival of long-stalled EU accession talks, as well as the quicker visa liberalization, the main prize in the eyes of many Turks.
Brussels aims to propose waiving visas for Turks on May 4 but that is strongly opposed by some EU member states. Ankara now meets just under than half of the 72 conditions for visa-free access.
"This is clearly shaping up to become a problem. We are talking about some criteria, while they seem to think they in fact already got visa-free travel," said one Brussels diplomat.
Turkish President Tayyip Erdogan has also put Merkel in a difficult position by demanding that Germany press charges against a comedian who recited a sexually crude satirical poem about him on a German public broadcaster last month.
Merkel's decision to let prosecutors pursue a case against Jan Boehmermann angered many Germans, who saw it as a sop to an authoritarian leader.
"As much as Davutoglu is trying to make this work, Erdogan seems to be going out of his way to test the limits of what he can get away with," a senior German official said.
"He is showing that he can do anything he wants, testing our reactions. That will be very difficult to handle."
A survey released on Friday showed that more than three in five Germans disapproved of Merkel's decision to agree to Turkey's demands over the comedian's case.
The poll was published by ZDF, the channel on which Boehmermann recited a poem suggesting Erdogan indulged in sexual perversions.
Critics argue that Merkel partly brought the problem on herself by telling Davutoglu on a phone call on April 4 that the poem was deliberately offensive.
"This was in retrospect a mistake," Merkel said during a news conference on Friday.
The ZDF also poll found that 80 percent of respondents doubted Turkey is a reliable partner in the migrant crisis.
Eight in 10 said Merkel respects Erdogan "too much".
Rights groups and some European politicians had already accused the EU of compromising its principles by striking the deal with Turkey at a time when its record on freedom of expression appears to be deteriorating.
Tusk said on Friday that the EU could discuss money to secure Ankara's help on migration but that the bloc's values, including freedom of expression, were non-negotiable.
"Recent experience with Turkey shows Europe must set clear limits to its concessions," Tusk said in an editorial published by seven European papers. [L5N17P3LD]
A senior Turkish government official said the Boehmermann case was likely to be discussed during Merkel's visit but that the main focus would be on relations with the EU and implementing the migrant deal, including how a promised 3 billion euros ($3.4 billion) in funding would be spent.
"We may not be able to say there is total agreement on everything between Turkey and the EU, but it is clear that there is common will. We’re not expecting a troublesome visit," the official said.
(Additional reporting by Orhan Coksun in Ankara, Jan Strupczewski in Brussels, Writing by Nick Tattersall, Editing by Ralph Boulton and Angus MacSwan)