The EU has begun a crucial summit on the migrant crisis, but a rift has already emerged on the closure of the main route through the Balkans.
A draft communique had revealed the EU was about to declare the route “now closed”, but the German government rejected this as “speculation”.
Turkey is also attending the summit, which is tackling Europe’s worst refugee crisis since World War Two.
The EU will press Turkey to take back migrants in return for $3.3bn in aid.
Last year, more than a million people entered the EU illegally by boat, mainly going from Turkey to Greece.
Many migrants leave Greece in a bid to reach northern Europe, but eight countries have introduced temporary border controls.
Some 13,000 migrants are currently stranded in northern Greece, after Macedonia, backed by Croatia, Hungary and Slovenia, closed its border to all but a trickle of migrants.
The human cost of the migrant crisis was brought home again on Sunday when a boat capsized off Turkey with the loss of 25 lives.
A Turkish search and rescue operation was launched after the latest sinking in the Aegean Sea.
At least three children are believed to be among those who died.
The International Organization for Migration (IOM) says at least 321 migrants drowned trying to get to Greece between 1 January and 3 March.
More than 2,000 migrants, most of whom the IOM says are from Syria, Iraq and Afghanistan, are arriving into Greece from Turkey every day hoping to travel further north through Europe.
But some EU countries re-imposed internal border controls and Macedonia sharply reduced the numbers allowed to cross, leading to a build-up on the Greek side of the border.
On Sunday, reports from the border said Macedonia had stopped allowing entry to anyone from areas in Iraq and Syria it did not consider to be active conflict zones.
As a result, anyone from Damascus or Baghdad is not allowed to pass.
Babar Baloch, a spokesman for the UN’s refugee agency, called the development “concerning”.
He said even some migrants from the Syrian cities of Latakia and Homs were being turned back. While a truce was signed between the Syrian government and rebels in Homs in December, the city remains a scene of devastation.
On Saturday, Apostolos Tzitzikostas, governor of a northern border region, said the number of migrants on the frontier waiting to cross north into Macedonia had grown to at least 13,000.
Mr Tzitzikostas called for a state of emergency to be imposed on the border that could facilitate the delivery of aid.
Last week, European Council President Donald Tusk said he had been told by the Turkish leader Recep Tayyip Erdogan that his country was ready to take back all migrants apprehended in Turkish waters.