The number of migrants arriving in Greece dropped 90 percent in April, the European Union border agency said today, a sign that an agreement with Turkey to control traffic between the two countries is working.

The agency, Frontex, said 2,700 people arrived in Greece from Turkey in April, most of them from Syria, Pakistan, Afghanistan and Iraq, a 90 percent decline from March.

Under the EU's agreement with Turkey, all migrants and refugees, including Syrians, who cross to Greece illegally across the sea are sent back.

In return, the EU will take in thousands of Syrian refugees directly from Turkey and reward it with more money, early visa-free travel and faster progress in EU membership talks.

In Italy, 8,370 migrants arrived through the longer and more dangerous route from northern Africa, Frontex said. Eritreans, Egyptians and Nigerians accounted for the largest share.

There was no sign migrants were shifting from the route to Greece to the central Mediterranean route, Frontex said. The number of people arriving in Italy in April was down 13 percent from March and down by half from April 2015.

That particular statement was contested by the Norwegian Refugee Council, an Oslo-based humanitarian agency. It cited Thursday's announcement by Italian coastguards that they had helped rescue 801 people, including many Syrians, from two boats heading from Northern Africa to Italy.

"This might be a first sign of Syrian refugees now choosing the much more dangerous route across the Mediterranean from Northern Africa to Italy, in search of protection in Europe," said Edouard Rodier, Europe director at the council.

"If this continues, the EU-Turkey deal is not only a failure, but may also result in more deaths at sea," he said in an statement emailed to Reuters.