Observers are bracing for what many believe could be a massacre in the Syrian city of Aleppo, the biggest by population in the country. Regime war planes have already bombed the city where rebels have assembled in an attempt to take and hold ground. Now artillery shelling is taking place, according to the rebels, and tank columns may be rolling in.

Another development is happening in the north of the country, near the border with Turkey:

President Bashar Assad, facing a growing rebel presence in Aleppo, Syria’s largest city and its commercial hub, has turned control of parts of northern Syria over to militant Kurds who Turkey has long branded as terrorists, prompting concern that Istanbul might see the development as a reason to send troops across its border with Syria.

Prime Minister Recep Tayyip Erdogan, in comments late Wednesday, said that Turkey would not accept an entity in northern Syria governed by the Iraq-based Kurdistan Workers Party, or PKK, which has long waged a guerrilla war against Turkey, and its Syrian affiliate, the Democratic Union Party.

He said the two groups had built a “structure in northern Syria” that for Turkey means “a structure of terror.”

“It is impossible for us to look favorably at such a structure,” he said in an interview with a private television channel.

He warned that if Syrian Kurdish militants mount a terror operation or some other form of cross-border provocation against Turkey, “then intervening would be our most natural right.”

It’s always worth pointing out that Turkey is a NATO member. They came close to requesting NATO support last month when one of their planes was struck down by Syrian anti-aircraft fire. Now Syria has created this safe haven for the PKK, perhaps inadvertently. Assad withdrew the forces from the northern regions to consolidate them in Aleppo. But if it leads to PKK cross-border operations inside Turkey, the Prime Minister said unequivocally that he would view that as an act of war and move to intervene militarily.

The risk of a protracted civil war in Syria is this kind of spillover effect throughout the Middle East, particularly in Lebanon and Turkey. Maybe this dies down; it’s not like Turkey has invaded Iraq over their PKK safe haven. But the risk has definitely been elevated.