DAMASCUS, Syria — Turkey said Sunday it was pursuing a military operation dubbed “Spring Shield” in northwest Syria after regime airstrikes on Thursday killed 34 Turkish soldiers.

The Syrian military threatened to down any aircraft over northwest Syria after Turkish drone strikes killed dozens of pro-regime forces in the embattled region.

“Syrian military high command announces the closure of the airspace for planes and any drone above northwestern Syria and especially above the Idlib region,” state news agency SANA reported a military source as saying.

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“Any aircraft breaching our airspace will be treated as enemy aircraft that needs to be downed and prevented from carrying out its goals,” the source said.

The Syrian Observatory for Human Rights said Turkish drone strikes killed 26 soldiers in northwest Syria on Saturday.

That brought the number of soldiers killed in Turkish drone strikes and bombardment since Friday to 74, said the Britain-based monitor, which relies on sources inside Syria.

Ten Hezbollah fighters and four allied militiamen also died, the Observatory said.

Since December, Russia-backed regime forces have led a military offensive against the last major rebel stronghold of Idlib in northwest Syria, where Turkey supports some rebel groups.

The onslaught has caused almost a million people — mostly women and children — to flee their homes and shelters, the United Nations says.

Neighboring Turkey already hosts around 3.6 million Syrian refugees, and is reluctant to let more in.

Tensions have spiked in recent weeks between Ankara and Moscow, whose relationship has been tested by violations of a 2018 deal to prevent a regime offensive on Idlib.

Turkey deployed troops to observation posts in northwest Syria under that deal.

Syria’s war has killed more than 380,000 people and displaced millions since it started in 2011 with the repression of anti-government protests.