Turkish artillery hit targets inside Syria for a second day Thursday after a mortar bomb fired from Syrian territory killed five Turkish civilians, according to Turkey's state media.

Meanwhile, NATO called for an immediate end to Syria's "aggressive acts."

In the most serious cross-border escalation of the 18-month uprising in Syria, Turkey hit back at what it called "the last straw" when a mortar hit a residential neighborhood of the southern border town of Akcakale.