DIKILI, Turkey (Reuters) - Turkey’s coastguard stopped nearly 200 people trying to reach Greece on Saturday, underlining the challenge security forces face in convincing migrants contemplating the voyage that they will not be allowed to enter the EU.

A controversial European Union deal to return refugees and migrants who landed on the Greek islands in the last fortnight to Turkey is due to take force on Monday.

A group of 118 Eritreans, Syrians, Iranian and Lebanese people were halted on Saturday as they headed to the Greek island of Chios from Cesme in Turkey in two dinghies, local news agency Dogan reported.

Another group of 63 were stopped as they attempted to travel to Greece’s Lesbos from the Turkish coastal town of Dikili. Reuters Television pictures showed the men, women and children sitting in a white tent after being caught, shielding their faces, with a heap of orange life-jackets piled outside.

Disagreements 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 been registered by Greek authorities 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.

But on Saturday the first modest signs of preparation were visible. Broadcaster CNN Turk showed a center being erected in Cesme where some returned migrants were expected to pass.

In Dikili, where migrants returned from Lesbos were due to be taken, two room-size tents were set up on the pier of its cramped port. Two portable toilets were installed nearby.

Dikili mayor Mustafa Tosun, who is from the opposition CHP party, told Reuters he wanted more help from the government. He said the General Directorate of Migration Management, which is responsible for the process, had sent two employees so far.

“They will check the ID of each refugee on a Turkish database in the port and then they will move on,” he said.

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 at our seaside.”

In September, the photograph of the body of three-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 five-year civil war.