'Brutal violence by regime must cease' in Syria: Washington

The U.S. on Wednesday called for an end to the violence in Syria after an airstrike hit a Turkish envoy, killing three civilians and injuring 12 others.

"Monday's reckless airstrike on a Turkish convoy follows similar vicious attacks by the [Bashar al-] Assad regime and its allies against civilians, humanitarian workers and infrastructure," State Department spokeswoman Morgan Ortagus said during a news briefing Wednesday. "This brutal violence must cease."

On Monday, the Turkish military initiated a troop transfer to Idlib to ensure the safety of an observation post, to keep supply routes open and prevent civilian casualties in the region, according to Turkey's Defense Ministry.

The ministry strongly condemned the airstrike, saying it "violates existing agreements, cooperation and dialogue with Russia."

Turkey and Russia agreed last September to turn Idlib into a de-escalation zone where acts of aggression are expressly prohibited.

The Syrian regime and its allies, however, have consistently broken the terms of the cease-fire, launching frequent attacks inside the area.

The de-escalation zone is currently inhabited by 4 million civilians, including hundreds of thousands displaced by regime forces from cities and towns throughout the war-weary country.

Hundreds of thousands of people have been killed and more than 10 million displaced during the course of Syria's more than eight-year conflict, according to the UN.