Greece's migration row with Austria intensified Friday, with Athens refusing a visit from Austria's interior minister whom it accused of "falsifying the truth" over its border control efforts.
A foreign ministry source confirmed a report by state news agency ANA that a request by Austrian Interior Minister Johanna Mikl-Leitner to visit Athens had been turned down.
"We confirm the report," the source told AFP.
The snub came a day after Greece recalled its ambassador to Vienna for consultations in retaliation for Austria's decision to leave Athens out of a Balkans migration meeting this week.
Austria has repeatedly accused Greece of failing to police its borders properly and allowing an excessively high number of migrants to continue their journey to western Europe.
At a meeting of EU interior ministers on Thursday, Mikl-Leitner called into question Greece's place in the passport-free Schengen zone.
"If it is really the case that the Greek external border cannot be protected, can it be still a Schengen external border?" she wondered.
An angry Greek Migration Minister Yiannis Mouzalas later retorted that Mikl-Leitner was "falsifying the truth" and "dragging Austria into increasingly hostile acts towards Greece and the EU."
"Our country guards its borders, which are also Europe's borders, in the best possible way. This is a fact confirmed by (EU border agency) Frontex, the European Commission and other institutions," Mouzalas said in a statement.
The Austrian interior ministry said Mikl-Leitner told her Greek colleagues in Brussels that she could come to Greece "to explain Austria's position in detail directly".
The ministry said it remained available "if Greece prefers to conduct the conversation at a later stage".
Greece believes Austria has encouraged a series of border restrictions by Balkan states along the migrant trail to northern and western Europe that has caused a bottleneck on its soil.
Thousands of refugees have been stranded in Greece after Macedonia denied all passage to Afghans and ramped up document controls for Syrians and Iraqis.
On Friday, there were some 4,000 people waiting to cross at the border post of Idomeni and some two dozen buses full of migrants parked a short distance away, local police said.
Macedonian police had only allowed some 150 people to cross since Thursday, Greek police said.
Greek authorities have been regulating the flow of refugees to the border but hundreds have set out on foot for the frontier, determined to continue their journey northwards, despite being told they will be turned back.
The government said efforts were under way to house migrants and refugees on the islands where they land by boat from neighbouring Turkey until the border situation is resolved.
"Three chartered ferries will remain -- if necessary -- at the ports of Lesbos, Chios and Samos as additional temporary accommodation facilities for the next two days," the merchant marine ministry said.
"The rate of transport of refugees and migrants on regular ferries will also be regulated," it added.
"We are trying to slow the flow (to the border) until a solution is reached," a migration ministry source told AFP.
Mouzalas on Thursday said Greece would not agree to "becoming Europe's Lebanon, a warehouse of souls" -- referring to the huge number of Syrian refugees Lebanon has taken in since 2011.
The migration crisis shows no signs of abating, with 100,000 arriving in Europe so far this year on top of the one million who made the journey in 2015, mostly across the Aegean Sea from Turkey to the Greek islands.
Slovenia on Friday said it wanted to limit the daily number of migrants entering at 580, in line with an agreement between police chiefs of countries along the Balkan route.
And Germany said it had been unable to locate some 130,000 people who had requested asylum last year.
Some may have returned to their home countries, travelled on to another country, or gone underground, Berlin said, adding that there may also have been repeated registrations of the same individual.
EU migration commissioner Dimitris Avramopoulos this week said the bloc's migration system could crumble if the number of migrants did not fall before a crucial meeting of EU leaders with Turkey in Brussels on March 7.
Failure to make progress with Turkey on stemming the migrant tide would spell "disaster" for the bloc, he warned Friday.
"If there is no convergence and agreement on March 7, we will be led to disaster," Avramopoulos told a conference in Delphi, central Greece.
He blasted "populist, nationalist and xenophobic" mentalities in certain EU countries, and noted that participants had left Thursday's interior ministers' meeting "particularly worried".
"We must end unilateral, bilateral and trilateral acts."
"If we believe that unilateral action is more effective than European action, then we are demolishing our common home," Avramopoulos said.