The Turkish defence ministry says two of its soldiers have been killed in northwest Syria in an attack by Syrian government forces, as fighting in the war-torn country's Idlib province continues on the eve of much-anticipated talks between the presidents of Turkey and Russia.

Following Wednesday's attack, which also left six Turkish troops wounded, Ankara's forces retaliated by striking Syrian military targets, the defence ministry said in a statement.

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It came a day after another Turkish soldier was killed by Syrian fire and nine others were wounded.

At least 59 Turkish soldiers have been killed in Idlib since Turkey began its military campaign in Syria's last rebel bastion, where a Russia-backed government offensive has forced nearly a million people to flee towards the shut Turkish border in search of safety.

On Sunday, Turkey, which backs certain rebel groups in Idlib, officially declared the start of a full-scale military operation against Syrian President Bashar al-Assad's forces.

Dubbed "Spring Shield", the operation came in response to the killing of 34 Turkish soldiers in Syrian government air raids last week, the biggest casualties suffered by Turkey's armed forces in decades.

Turkey has since downed three Syrian fighter jets and killed dozens of government soldiers and allied fighters - mostly through drone attacks, according to monitors.

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Turkey has sought to push back Syrian government forces behind lines agreed under a 2018 deal with Russia, which established 12 Turkish observation posts and created a de-escalation zone around the province, which is home to more than three million people.

On Wednesday, President Recep Tayyip Erdogan called the operation "a historic struggle", adding that Ankara will not forsake oppressed Syrians.

Al Jazeera's Sinem Koseoglu, reporting from Cilvegozu on Turkish-Syrian border, said the Turkish government is becoming increasingly vocal about the necessity of its military campaign.

"Officials say that Turkey is in Syria to protect its borders and millions of innocent civilians suffering from the Syrian government's atrocities in the region," she said.

Turkey, which already hosts some four million refugees, wants to prevent another influx from Idlib.

It has pressured the European Union for greater assistance by announcing that migrants and refugees would no longer be prevented from trying to enter the bloc via the Greek border.

A Turkish military convoy near the town of Batabu on the highway linking Idlib to the Syrian Bab al-Hawa border crossing with Turkey [Aaref Watad/AFP]

Key Moscow meeting

On Thursday, Erdogan will try to reach a deal on a ceasefire over Idlib when he meets his Russian counterpart, Vladimir Putin, in Moscow.

A day before the meeting, Russia, al-Assad's main ally in Syria's long-running war, accused Turkey of breaching the 2018 agreement.

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Its Ministry of Defence said on Wednesday that fortified rebel positions in Idlib had merged with Turkish observation posts, and that artillery attacks on nearby civilian areas and Russia's airbase in Syria had become a daily occurrence.

Turkey has not yet commented on the Russian claims.

Al Jazeera's Step Vaessen, reporting from Moscow, said the allegations were likely to increase tensions before the Thursday's talks.

"The statement is meant to position Russia a day before the meeting. It is taking a very hard position towards Turkey," she said.

Kremlin spokesman Dmitry Peskov said on Wednesday the Kremlin hoped Putin and Erdogan would be able to agree on a set of joint measures in Idlib.

Syrian government forces, supported by Russian airpower, have retaken swathes of territory since launching their offensive in December, killing hundreds of civilians and causing a massive wave of displacement.

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The United Nations has described the situation in Idlib as the "biggest humanitarian horror story of the 21st century" and called for an immediate ceasefire.

Despite being on opposite sides of the war, Ankara and Moscow have kept lines of negotiation open.