Merkel's visit to the Nizip camp -- a sprawling complex where migrants are housed in tents and metal containers, about 30 miles east of the southern Turkish city of Gaziantep -- is intended to counter opponents of the deal, which has been criticized by human rights groups.
A tweet from European Council President Donald Tusk included a photo of Merkel and others being greeted with flowers presented by young women in white dresses: "Visiting victims of Syria war at #Nizip refugee camp in Turkey."
Prime Minister Ahmet Davutoglu led the EU representatives on a tour of the camp, where they greeted children and inspected living conditions. They also inaugurated a child protection center in Gaziantep.
European Commission First Vice President Frans Timmermans told reporters the camp was evidence of the "commitment of the Turkish people to accommodate en enormous influx of refugees."
"I think we, as Europeans, should state very clearly today that you are not alone in this," he said.
Merkel spoke about Syria's fragile ceasefire.
"Syrians tell me they wish to go back home and, of course, we wish to drive forward the peace process," she said at a news conference.
"This shows our urgency. All parties need to be prepared for a compromise and everyone needs to be involved in talks."
The refugee crisis and peace process are connected, Merkel said.
"People, of course, who feel safe, do not need to leave their home country," she said.
Under the terms of the March 18 agreement between the EU and Turkey, migrants who cross into Greece illegally after March 20 are being sent back to Turkey.
For every Syrian sent back to Turkey under the plan, a vetted Syrian refugee will go from Turkey to Europe to be resettled, although the maximum number is capped at 72,000 people. In return, the EU will give Turkey billions in funding to help it provide for the migrants within its borders, and grant various political concessions.
More than 1 million people made "irregular arrivals" inside Europe's borders
in 2015 alone, many of them displaced by the Syrian civil war.
By comparison, about 2.7 million Syrian refugees are registered in Turkey.
A sign outside the camp visited by EU officials Saturday said, "Welcome to the world's largest refugee hosting country."
Human rights group criticizes deal
A report released by Amnesty International
earlier this month condemned the EU agreement and accused Turkey of forcibly sending people back to Syria, constituting a violation of international law -- a charge Turkey denies.
The report said it found many cases of large-scale returns from the Turkish province of Hatay, and called it an "open secret in the region."
"In their desperation to seal their borders, EU leaders have willfully ignored the simplest of facts: Turkey is not a safe country for Syrian refugees and is getting less safe by the day," said John Dalhuisen, Amnesty International's director for Europe and Central Asia.
A statement from the Turkish foreign ministry said the Amnesty International report "does not reflect the truth."
Turkey had been observing an "open door policy" for five years with regard to refugees, and complying with the principle of "no returns," the ministry said.
Crowded, harsh conditions
About 15,000 people live in the camps at Nizip. Many more live in other camps in Turkey, as well as some on the Syrian side of the border, established as Turkey has tried to keep its refugee burden under control.
The Nizip camp is less than 20 miles from the Syrian border.
Turkey shares a 560-mile border with Syria and has borne the brunt of the exodus of Syrians since the civil war began there in March 2011.
Many Syrian refugees at the camps hope to move on. Speaking Arabic, not Turkish, they do not feel at home -- and Turkey is not particularly welcoming to them.
Until now, Turkey has been happy to be merely a transit point for the migrants.
But now, under the new EU deal, the country has agreed to take back all virtually all irregular migrants from the Greek islands. The carrot offered in exchange is the prospect of visa-free travel for Turks to the European Union.