Turkish President Recep Tayyip Erdogan accused Moscow of "not honoring" agreements made with Ankara to stem the conflict in northwestern Syria where Russian and Syrian warplanes have increased their assault.
"There have been agreements made with Russia. If Russia honors these agreements, we will do the same. But right now, unfortunately, Russia is not honoring these deals," Erdogan said, quoted by the Hurriyet daily.
Despite being on opposite sides of the war, Damascus ally Moscow and opposition supporter Ankara have worked closely to resolve the conflict.
This was a rare critical remark from Erdogan who has often sought to keep good relations with Russian President Vladimir Putin since a 2016 rapprochement.
But violence has raged in the last opposition stronghold of Idlib in spite of a 2018 Turkey-Russia agreement signed to prevent a full-scale Syrian offensive.
The deal was made in the Russian resort of Sochi.
There have been numerous ceasefires for the region home to some three million people, including one sponsored by Moscow and Ankara earlier this month.
Yet eight civilians were killed Thursday by Russian airstrikes in Idlib, a region to which many people fled after being displaced from other former rebel-held areas.
As part of the Sochi deal, Turkey set up 12 observation posts, one of which was surrounded by Syrian President Bashar al-Assad's forces in December.
Erdogan said Turkish officials continued their talks with Russian counterparts, adding that they had said that Turkey's "patience was running thin."
The president then delivered the warning given to Moscow that Turkey "would do whatever is necessary" if the bombing in Idlib does not stop.
The Turkish defense ministry Tuesday said Turkey would retaliate in self-defense if any of the posts were threatened.
One of Ankara's major fears is of a refugee influx to Turkey from those fleeing violence.
But Erdogan on Sunday said Turkey was working on constructing homes inside Syria after the United Nations said nearly 360,000 people had been displaced.
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