GAZIANTEP, Turkey -- Turkey's prime minister said Saturday the number of migrants crossing into Greece illegally has dropped considerably, as proof that a much criticized migration deal between Turkey and the European Union is working.

Ahmet Davutolgu was speaking at a joint news conference with German Chancellor Angela Merkel and top European Union officials who travelled near Turkey's border with Syria in a bid to promote the troubled deal with Turkey as they face increasing pressure to reassess the agreement. The group toured a refugee camp and inaugurated a child support centre funded by the EU.

European Union Council President Donald Tusk said the EU plans to spend 1 billion euros ($1.1 billion) on projects this summer to improve the lives of Syrian refugees in Turkey and Davutoglu said the bloc has already launched projects worth 187 million euros ($211 million).

Human rights groups criticized the trip to what they call a "sanitized" refugee camp -- and said EU officials should look further at the tens of thousands of Syrian refugees that are now blocked from entering Turkey.

Many have questioned the legality of the March 20 EU-Turkey deal allowing for the deportation of migrants who don't qualify for asylum in Greece back to Turkey.

Davutoglu said the number of migrants crossing illegally into Greece had dropped from around 6,000 per day in November to around 130 daily since the beginning of this month.

"This drop shows the effectiveness of this joint mechanism," Davutoglu said.

"Our priority was to stop the baby Aylans from washing up on the shores, and we have made great strides in this aim," Davutoglu said, in reference to drowned 3-year-old Aylan Kurdi, whose images helped galvanize world attention on the plight of the migrants.

In return for the deal, the EU has earmarked 6 billion euros ($6.8 billion) to Turkey over the next four years to help improve conditions for the 2.7 million Syrian refugees inside Turkey. The EU is also set to allow visa-free travel for Turkish citizens.

Rights groups, EU legislators and the U.N. refugee agency have questioned the moral and legal implications of expelling people from Greece back to Turkey -- a country that many consider unsafe on grounds of security and human rights.

Despite insisting that it has an open-door policy for Syrian refugees, Turkey in the past few months has blocked several thousand refugees who were fleeing northern Syria at the border, providing aid to them at displaced persons camps near the border instead. Human rights groups say some of the camps have been attacked and are pressing Ankara to give the refugees shelter inside Turkey.

Amnesty International says Turkish authorities have also for the past three months been expelling around 100 Syrians a day back to their war-ravaged country -- an accusation Turkey has denied. The country has also rejected claims that Turkish soldiers have sometimes shot at refugees trying to cross the border illegally.

Davutoglu reacted angrily to the Amnesty claim Saturday, saying not a single Syrian had been returned to his or her homeland without consent.

Tusk backed Turkey, saying the country -- which is host to the worlds' largest refugee population -- was "the best example in the entire world of how to treat refugees."

On Syria, Merkel said she was in favour of the creation of "areas that are under special protection of the cease-fire, where as much safety as possible can be offered."

Merkel said: "The safer people can feel, the less they have to leave their homeland."

Earlier, New York-based advocacy group Human Rights Watch urged EU leaders to understand the whole refugee picture at the Turkish border.

"Instead of touring a sanitized refugee camp, EU leaders should look over the top of Turkey's new border wall to see the tens of thousands of war-weary Syrian refugees blocked on the other side," said Judith Sunderland, Human Rights Watch's acting deputy Europe and Central Asia director. "Then, they should go to the (Turkish) detention centre for people who were abusively deported from Greece. That should make them rethink the flawed EU-Turkey deal."

Merkel's visit also comes amid controversy over her decision to grant Turkey's request to let German prosecutors and courts decide whether German comedian Jan Boehmermann had insulted Turkish President Recep Tayyip Erdogan. Critics have accused Merkel of kowtowing to Turkey because of the country's important role in stopping the influx of migrants to Europe.

Merkel denied that Germany was no longer raising the question of freedom of expression with Turkish leaders.

"I can assure you that the fact we speak with each other so often -- much more often than we used to -- leads to our addressing all these issues," she said.

Turkey's leaders have warned that the entire migrant deportation deal will collapse if the EU fails to grant Turkish citizens the right to visa-free stays for tourism or business by July. On Saturday, Davutoglu said the issue was "crucial" for Turkey and said his country was working to fulfil its commitments on the issue.

Meanwhile, U.S. President Barack Obama also weighed in on the issue in comments to German daily Bild that were published Saturday. He praised Merkel's "political and moral leadership" in the migrant crisis, but also stressed the need to uphold human rights.

"The recent agreement between the EU and Turkey is a step toward a more equitable way of sharing this responsibility," he said. "As the agreement is implemented, it will be essential that migrants are treated properly and that human rights are upheld."

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Suzan Fraser reported from Ankara, Turkey. Geir Moulson in Berlin and Derek Gatopoulos in Athens contributed to this report.