Image source, Getty ImagesImage caption, Thousands of people, many of them Kurds arriving from the Middle East, are camping at the border with Poland
Turkish authorities have stopped all citizens of Iraq, Syria and Yemen from flying from Turkey to Belarus, until further notice.
Turkey's Civil Aviation Authority said it was because of illegal migrant crossings from Belarus into the European Union.
The UN Security Council has accused Belarus of using the migrants to destabilise the EU's eastern border.
The EU is lobbying countries in the Middle East to take similar measures.
Belarus's authoritarian leader Alexander Lukashenko has threatened to cut off gas supplies to Europe if new sanctions are imposed.
Meanwhile, Belarusian and Russian paratroopers have staged joint drills near the Polish and Lithuanian borders.
Russia is Belarus's main ally and has rejected the accusations made by the EU.
Thousands of people, many of them Kurds arriving from the Middle East, are camping at the border with Poland, enduring freezing conditions in the hope of crossing into the EU. The migrants are mainly young men.
Crowds have tried to cut through a barbed wire fence to enter Poland this week – only to be pushed back by Polish border guards and the army. However, some migrants have managed to slip through.
Overnight temperatures have fallen to freezing and at least seven people have died in recent weeks, many from hypothermia.
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Turkey banned Syrian, Yemeni and Iraqi citizens from flights to the Belarusian capital, Minsk, on Friday.
This could block one of the routes used by migrants that the EU says have been flown in by Belarus to create a deliberate humanitarian crisis on its frontier.
The EU accuses Belarus of manufacturing the crisis by distributing Belarusian visas in the Middle East, flying in the migrants and urging them to attempt crossing the border illegally.
Mr Lukashenko denies this and said his country would have to respond if the EU imposed a fifth series of sanctions.
The EU says he started luring migrants in retaliation for sanctions imposed over his brutal crackdown of protesters and critics. Belarusians took to the streets last year after he claimed a widely discredited election victory.
Iraq has said it is organising repatriation flights for Iraqi nationals from Belarus.
The EU is also reportedly considering sanctions against the Russian state airline Aeroflot for transporting migrants to Belarus, an allegation Aeroflot denies.
Image source, ReutersImage caption, The migrants are mainly young men – but there are also women and children
Russia and Belarus staged drills on Friday at the Gozhsky training ground. The drills included searching and destroying enemy targets, the Belarusian defence ministry said.
On Thursday, German Chancellor Angela Merkel discussed the build-up of migrants with Russian President Vladimir Putin, for a second day running. He has urged the EU to restore contacts with Belarus in order to resolve the crisis.
Mr Lukashenko's threats to cut off gas supplies to Europe raised fresh fears amid worsening natural gas shortages and rising prices on the continent.
Belarus receives significant transit fees for the pipelines transporting Russian gas to the EU. Any decision would have to be approved by Russia, which is anxious for its new Nord Stream 2 pipeline to Germany to be certified.
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