Turkey's Coast Guard stopped 63 Palestinians and Syrians trying to cross to a Greek island on Saturday, underlining the scale of the security forces' task in convincing illegal migrants they won't be allowed into the EU.

A controversial European Union deal to return rejected asylum seekers to Turkey is due to go into action on April 4.

The group stopped on Saturday was trying to cross to the Greek Island of Lesbos from the Turkish town of Dikili on the Aegean coast. The men, women and children were seen sitting in a white tent, shielding their faces, with dozens of orange life jackets piled outside.

Disagreement over how to deal with hundreds of thousands of migrants from Syria and elsewhere threatens to tear the 28-nation EU apart, making the deal with Turkey critical to resolving the crisis.

Turkey agreed last month to take back all migrants and refugees who crossed informally into Greece after March 20 in exchange for financial aid, visa-free travel for Turks and slightly accelerated bloc-membership talks.

Thousands of migrants are still attempting the dangerous sea crossing, although arrivals have slowed. More than 1,900 people have reached Greece so far this week despite poor weather conditions, and a total of 5,622 have registered since March 20.

With Turkish authorities silent on their plans, uncertainty remained over how many will be sent back, how they will be processed and where they will be housed.

Some were expected to pass through Dikili, returning from Lesbos, one of the closest Greek islands to Turkey. No preparations were visible in the town, and no area dedicated to holding them was reserved.

Nevertheless, a few hundred people turned out to a protest against a refugee camp in the small town. Others said refugees should be kept at the main camps close to Syria.

Some waved Turkish flags, and a few chanted: "We don't want to see dead babies' bodies on our seaside."

In September, the photograph of the body of 3-year old Syrian boy Aylan Kurdi found washed up on a Turkish beach sparked global outrage at the perceived inaction of developed nations in helping refugees, many of whom have fled Syria's four-year civil war.