The Turkish Parliament is debating a bill that would authorize military action inside Syria's borders as it continues to trade shelling with its neighbor. Artillery fire from Turkey into Syria has reportedly killed several Syrian soldiers in response to a mortar attack that left five Turkish civilians dead on Wednesday.
To be clear, the bill would not be a declaration of war against Syria, but would give the Turkish military permission to move across the border and engage Syrian troops directly, should the need arise. That's not a scenario that anyone in Turkey really wants, but it can't afford to do nothing as Damascus continually threatens its border. It's more of a warning to Bashar al-Assad to back off and not risk escalating his civil war into an international one. It may also be a subtle reminder that as a member of NATO, starting a war with Turkey means (theoretically) starting a war with half of Europe and the United States. The last thing Syria wants is to give those nations an excuse to get involved, though Assad may also be wagering that the United States will do anything to avoid a military adventure so close so its upcoming election.
Still, as long as Turkey remains a base of operations for Syrian rebels, tensions will remain high. Even Israel is now concerned that "armed Syrians" are wandering a little too close to its border on the Golan Heights. The only thing that seems clear at the moment is that the situation is deteriorating on all sides and the biggest side—Syria shares Turkey's longest international border—can only stay quiet for so long.
Update 7:50 a.m.: Turkey's parliament did indeed pass the resolution, giving the prime minister the authority to order troops into Syria without further authorization.
Update 9:30 a.m.: Syria has admitted that it fired shells into Turkey and has apologized for the death of five civilians, according to the AP. That may cool tensions off for now.