BRUSSELS -- German Chancellor Angela Merkel and top European Union officials plan to travel close to Turkey's border with Syria in hopes of promoting a troubled month-old agreement to manage a refugee crisis that has left hundreds of thousands stranded on the migrant trail to Europe.

Saturday's trip to the Turkish border city of Gaziantep, which is expected to include a visit to a refugee camp, comes amid questions over the legality of the March 20 agreement between the EU and Turkey to start deporting migrants who do not qualify for asylum in Greece back to Turkey.

The EU has pledged up to 6 billion euros ($6.8 billion) in aid to Turkey over the next four years to ease conditions and create opportunities for the estimated 2.7 million Syrian refugees living in Turkey.

But a month after the agreement was signed, few EU experts have arrived in the field and many EU nations are dragging their heels on accepting more asylum-seekers. Diplomatic tussles loom over Turkey's demands for visa-free EU travel for Turkish citizens.

In an effort to persuade European and Turkish citizens of the deal's merits, Merkel, EU Council President Donald Tusk, EU Commission Vice-President Frans Timmermans and Turkish Prime Minister Ahmet Davutoglu plan to gather in Gaziantep across the border from the Syrian cities of Aleppo and Kobane, epicenters for years of civil war that have abated since a shaky February cease-fire agreement.

The U.N. refugee agency, rights groups and EU lawmakers have roundly criticized the EU-Turkey migrant deal over the legal and moral implications of expelling people from EU member Greece back to Turkey, a country that many consider unsafe on security and human rights grounds. Merkel has found herself in a particular bind, backing the deal even as Turkish President Recep Tayyip Erdogan uses an arcane law to sue a German comedian for mocking him.

The 47-nation Council of Europe, a human rights body that is not part of the EU, passed a resolution Wednesday criticizing the EU-Turkey deal for what it called "several serious human rights issues."

Not far from Gaziantep, Turkish authorities have been expelling around 100 Syrians almost daily back to their war-ravaged homeland for the past three months, according to rights group Amnesty International. Turkey insists that it does not deport Syrians.

Only about 10 per cent of Turkey's refugees are sheltered in camps. The rest primarily fend for themselves in towns and cities.

The European Commission says the number of migrants arriving in Greece from Turkey has slowed dramatically from more than 50,000 in February to around 7,000 over the past 30 days. But Greece, currently home to 54,000 stranded migrants seeking to travel deeper into Europe, faces unrelenting pressure as the long-promised relocation of asylum seekers from Greece to other EU countries moves pitifully slowly.

When Pope Francis took a dozen Syrians to the Vatican from the island of Lesbos last weekend, he effectively relocated more refugees from Greece than more than a dozen EU countries have managed since September under an earlier European plan to share responsibility for 160,000 refugees in Greece and Italy.

Since last month's pact, 325 migrants in Greece have been returned to Turkey, only two of them Syrians. In the other direction, 103 Syrians have been delivered from Turkey to Europe.

The EU's border agency Frontex requested 1,550 reinforcements a month ago to help police the deal, but so far just 340 officers and experts have been deployed. The EU's asylum agency requested almost 900 officers and interpreters, but only 130 have been sent.

Legal issues remain unresolved. While Turkey has upgraded human rights protections for Syrians returned from Greece, it has yet to offer the same guarantees to the much more numerous Afghans, Iraqis and Eritreans who are being returned from Greece and could qualify for the same protection under international asylum laws.

EU nations and the European Commission have made some 2.6 billion euros available so far. Once the 3 billion mark is reached, and if that money is spent in accordance with the agreement, a further 3 billion euros could be provided in 2018. So far, the main payments in March have been 40 million euros to the World Food Program for six months' worth of meals in refugee camps, and 37 million euros to UNICEF to support school enrolment for refugee children.

Part of the EU fund is being used to try to ensure that all 850,000 school-aged children are enrolled in schools in September, a senior Turkish official said. Currently only 330,000 are in school.

Turkey's leaders are warning that the whole deal will collapse if the EU fails to grant Turkish citizens the right to visa-free stays for tourism or business purposes by July.

The agreement stipulates that Turkey must meet 72 conditions by May 4 to earn the visa waiver. So far it has fulfilled about half. EU officials say Ankara is making good progress but suggest that all conditions might not be fulfilled on time, including upgrading Turkey's visa system and bringing its data protection laws into line with EU standards.

"If the European Union does not take the steps it needs to take, if it does not fulfil its pledges, then Turkey won't implement this agreement," Erdogan warned earlier this month.

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Soguel reported from Istanbul. Associated Press reporter Suzan Fraser in Ankara, Turkey, contributed to this story.