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The warning came after 33 Turkish soldiers were killed by airstrikes in northern Idlib province on Thursday. Turkey has blamed Russia.
Turkish action in Syria is just one part of a chain reaction that experts believe could lead to another humanitarian crisis in Europe.
The mayor of Bolu said he would arrange the buses for "whatever the number [of refugees]" who needed the service and wanted to travel on to Europe.
This week in pictures: COVID-19 spreads in Europe, Syrians flee violence and Greek protests
Turkey says it will not back down in a stand-off with Russia over the northern Syrian region of Idlib.
More than 900,000 people have been displaced by violence in northwest Syria in fewer than three months.
Turkish President Recep Tayyip Erdogan has announced he would hold a summit with his Russian, French and German counterparts on 5 March to discuss the situation in Idlib province, the last rebel stronghold in northwestern Syria.
The UN human rights office wants safe corridors for civilians trying to flee fighting in Syria's northwest and who 'no longer have anywhere to go'.
The Kremlin hit back at Ankara, accusing it of disregarding its commitment under the agreement to stabilise the region.
A wave of displacement that has seen around 700,000 people flee a regime offensive in Syria's Idlib region is the biggest of the nine-year-old conflict, the United Nations said on Tuesday.
Guterres said conflicts in Libya, Yemen and Syria were escalating as gains made in 2019 are reversed in 2020.
Weeks of intensive aerial bombardment has sent huge numbers fleeing northwards closer to the Turkish border.
Turkey's foreign minister says Ankara and Moscow are working to keep peace efforts for Syria alive despite a deadly clash between Turkish and Syrian forces
The industrial giant is still accused of financing terror groups including IS as it tried to keep its Syrian plant open amid the conflict.
The comments come after Interior Minister Suleyman Soylu said Turkey could return militant prisoners to Europe.
Sayfoellah, Shahied, Muthanna and Mujahied – seen in the video above – are missing after the detention camp in which they were being held in north-east Syria was forcibly evacuated, their grandmother has told Euronews.
Human rights activists applauded as Germany charged two alleged former Syrian secret service officers with participating in crimes against humanity,
European leaders are warning that the fight against terrorism is far from being over following the death of Abu Bakr al-Baghdadi. The world's most wanted terrorist, and leader of the so-called Islamic State group killed himself during a US military operation in Idlib, northern Syria