After months of railing against the gains by the Kurdish YPG in northern Syria, Turkish army forces began shelling YPG targets in earnest this weekend, and pretty quickly escalated their involvement to begin attacking the Syrian military in northern Aleppo Province as well.

Turkish officials insist they had set rules of engagement to defend the rebel-held border town of Azaz, and also demanded that the Kurds cede the Menagh Air Base back to the Levantine Front, an Islamist faction that took it from last week.

Turkey has long used the Azaz crossing to funnel aid to rebel factions, and has expressed concern as both the Syrian military and the Kurds have made gains in the area, saying they would not allow the Kurds in particular to hold the area.

Turkish officials are talking up the possibility of escalating their involvement to include ground troops, and the Syrian government says it believes the first Turkish troops may already have arrived, as around 100 gunmen crossed the border at Azaz, and they believe some are Turkish military forces.

The sudden Turkish attacks come just days ahead of the start of a ceasefire in Syria, and the US and some European nations are urging Turkey to knock it off, though PM Ahmet Davutoglu insists Turkish strikes will continue as a “necessary response” to the Kurdish gains.