The rebels who are trying to bring down Assad have used Turkey as their base, enraging a regime that accuses foreign countries of fomenting the unrest inside Syria.
The spark for the latest hostility was a mortar shell fired from Syria that slammed into a house in the Turkish border village of Akcakale on Wednesday, killing two women and three children.
"[The shell] hit my neighbor next door. His wife, his children died," villager Bakir Kutlugil said. "Now I worry whether the next one will hit me or my neighbor."
The Turkish response to the Syrian shelling was swift - it fired salvos of artillery rounds inside Syria, contacted its NATO allies, and convened parliament for a vote authorizing further cross-border military operations if necessary.
The bill opens the way for unilateral action by Turkey's armed forces inside Syria. Turkey has used a similar provision to repeatedly attack suspected Kurdish rebel positions in northern Iraq.
The U.N. Security Council unanimously approved a statement condemning Syria's shelling of the Turkish village "in the strongest terms."
Council members managed to bridge differences between the strong statement demanded by the United States and its Western supporters and backed by their NATO ally Turkey, and a weaker text pushed by Russia, Syria's most important ally, after negotiations that began late Wednesday and continued through Thursday.
The council demanded an immediate end to such violations of international law and called on the Syrian government "to fully respect the sovereignty and territorial integrity of its neighbors."
Syria's U.N. envoy said Thursday that his government was investigating the source of the shelling and did not want any escalation of violence with Turkey.
Ambassador Bashar Ja'afari said the Assad regime sent its "deepest condolences" to the families of the victims, but stopped short of an apology, pending the outcome of the investigation. He also urged Turkey to act "wisely, rationally" and prevent infiltration of "terrorists and insurgents" and the smuggling of arms across the border.
Turkish Prime Minister Recep Tayyip Erdogan said Thursday that Turkey did not want war with Syria but was determined to protect its borders and its people.
"We want peace and security and nothing else. We could never want to start a war," Erdogan said.