"The approach of not intervening against migrants wishing to leave Turkey remains in practice but this (new) approach covers sea crossings because of the dangers," Turkish coastguard tweeted.
President Recep Tayyip Erdogan has ordered the Turkish coastguard to prevent migrants crossing the Aegean Sea because of the risks, officials said.
"On the orders of the president ... permission will not be given for migrants to cross the Aegean Sea because it is dangerous," the coastguard tweeted on Friday.
The coastguard said 97 migrants were rescued on Thursday after "the Greek side flattened three boats and left them in a half-sinking state in the middle of the sea."
"The approach of not intervening against migrants wishing to leave Turkey remains in practice but this (new) approach covers sea crossings because of the dangers," it added in another tweet.
The instruction comes after Erdogan said last week that refugees and migrants would not be prevented by Turkish authorities from leaving Turkey if that was their wish.
Thousands of migrants headed for Turkey's land border with Greece after the Turkish government said last week that it would no longer prevent migrants and refugees from crossing over to EU territory. Greece deployed riot police and border guards to repel people trying to enter the country from the sea or by land.
Tear gas shot two ways over migrants at Turkey-Greece border
President Erdogan plans to be in Brussels on Monday for a one-day working visit, his office said amid a charged conflict between Turkey and the European Union over migrants and refugees.
A statement from Erdogan's office said he would travel to Brussels on March 9. The statement did not specify where he would be during his one-day visit or the nature of the work taking him to the Belgian capital, but the European Union's headquarters are in Brussels.
The announcement came hours after European Union foreign ministers meeting in Croatia on Friday criticised Turkey, saying it was using the migrants' desperation "for political purposes."
Clashes at border
More clashes erupted on Saturday between Greek police and Europe-bound migrants gathered on the Turkey side of a border crossing near the Greek village of Kastanies. Like previous confrontations this week, officers in Greece fired tear gas to impede the crowd and Turkish police fired tear gas back at their Greek counterparts.
A Greek government statement issued on Saturday said that around 600 people, aided by Turkish army and military police, threw tear gas at the Greek side of the border overnight. There were several attempts to breach the border fence, and fires were lit in an attempt to damage the barrier, the statement said.
“Attempts at illegal entry into Greek territory were prevented by Greek forces, which repaired the fence and used sirens and loudspeakers," the statement read.
The Greek police also used water cannons to stop the migrants, a correspondent said, many of whom have been stranded for days at the Pazarkule border, known as Kastanies on the Greek side.
Erdogan announced last week that Turkey, which already houses more than 3.5 million Syrian refugees, would no longer be Europe's gatekeeper and declared that its previously guarded borders with Europe are now open.
The move alarmed EU countries, which are still enduring political fallout from a wave of mass migration five years ago.
Erdogan calls on EU to share burden
Erdogan has demanded that Europe shoulder more of the burden of caring for refugees.
To date, Turkey has spent over $40 billion on handling the refugee crisis, much of which has gone into providing refugees with safe places to live, and primary, secondary, and tertiary education.
European leaders promised Turkey a total of six billion euros, paid in two instalments of three billion euros each. Turkey has only confirmed receipt of the first payment.
But the EU insists it is abiding by a 2016 deal in which it gave Turkey billions in refugee aid in return for keeping Europe-bound asylum-seekers on its soil.
In a phone call with German Chancellor Angela Merkel on Friday, Erdogan said the Turkey-EU migration deal is no longer working and needs to be revised, according to the Turkish leaders's office.
The European foreign ministers acknowledged Turkey for hosting millions of migrants and refugees, but said the 27-nation EU “strongly rejects Turkey's use of migratory pressure for political purposes." The ministers called the situation at the Greece-Turkey border unacceptable and said the EU was determined to protect its external boundaries.
Greek authorities said they thwarted more than 38,000 attempted border crossings in the past week and arrested 268 people — only 4 percent of them Syrians. They reported 27 more arrests on Saturday, mostly of migrants from Afghanistan and Pakistan.
Greece has described the situation as a threat to its national security. In response it has suspended asylum applications for a month and said it will deport new arrivals without registering them. Many migrants have reported crossing into Greece, being beaten by Greek authorities and summarily forced back into Turkey.
Accusations over mistreating migrants
Turkish authorities say one migrant was killed by bullets fired by Greek police or border guards near the border crossing. Greece denies the accusation. A child also drowned off the island of Lesvos when a boat carrying 48 migrants capsized.
On Saturday, Turkish Interior Minister Suleyman Soylu renewed accusations of Greek authorities mistreating migrants.
“Their masks have fallen. The ruthlessness of those who gave lectures on humanity has become evident," Soylu said.
Soylu claimed that some 1,000 Turkish special operations police deployed on the border had started to thwart the actions of the law enforcement teams assembled by Greece to drive the migrants back.
The minister also predicted that Greece would not be able to “hold on to its borders" during the summer, when the river that delineates most of the Turkey-Greece border gets shallower and easier to cross.
Soylu has said Erdogan instructed Turkish authorities to prevent migrants from attempting to reach the Greek islands in dinghies to avoid “human tragedies." Hundreds have drowned attempting the comparatively short but dangerous voyage from Turkey's coast.
Greece to build new camps after migrant surge
Greece plans to build two new temporary camps to house hundreds of additional asylum seekers who arrived after a surge enabled by Turkey, the migration minister said on Saturday.
"We want to build two closed centres in (the northern region of) Serres and the greater Athens area with 1,000 places," migration Minister Notis Mitarachi told Skai TV.
"We need the backing of local communities. We cannot leave all (these) people on the islands," he said.
Mitarachi said the camps would host asylum seekers who arrived after March 1, when Turkey announced it would no longer prevent people from trying to cross into the European Union.
Residents of Serres town, rumoured to host one of the camps, staged protests earlier this week and local officials declared their opposition to the plan.
Over 1,700 migrants have landed on Lesvos and four other Aegean islands from Turkey over the past week, adding to the 38,000 already crammed into abysmal and overstretched refugee centres.
The new surge has ramped up already high tensions on an island that has been on the migration frontline for years.
Frustration exploded into violence last weekend with mobs setting up roadblocks, attacking cars carrying NGO workers and beating journalists.