Macedonia's president says Greece is not being cooperative on the immigration crisis following a large influx of refugees into his country on Monday.
Gjorge Ivanov convened a meeting of the National Security Council late on Tuesday, and afterwards told the press that Greece should stop allowing migrants to reach the boundary between the two nations.
About 14,000 people are stuck in a muddy tent city at the Idomeni crossing, on the Greek side of the border, hoping that Macedonia will allow them through on their journey to Europe's prosperous heartland.
About 1,500 bypassed a fence on Monday to enter Macedonia, but were detained and forced back into Greece - with violence according to some refugees. Macedonia has rejected the claims.
Mr Ivanov called for better cooperation between Macedonian and Greek security services.
Meanwhile, the UN refugee agency says more than one million people have crossed into Greece alone since the start of 2015.
UNHCR figures show more than 143,500 people - mostly Syrians, Iraqis and Afghans - have reached Greece from Turkey this year through March 14.
A calculation of agency figures Wednesday shows total land and sea arrivals into Greece were 1,000,229 since January 1, 2015.
UNHCR and the International Organisation for Migration had previously reported that more than one million people reached Europe overall last year, but that included arrivals across the central Mediterranean route from Libya to Italy.
The new figures show how much Greece has borne the brunt of the influx. UNHCR has repeatedly appealed to the European Union to take a more coordinated approach in handling the influx.