On October 3, Syrian military forces reportedly fired a mortar round that landed in Turkey, killing five civilians and wounding ten or more in the border town of Akcakale. In retaliation, Turkish artillery shelled the locations from which Syrian forces had fired, apparently using counterbattery radar. The Turks renewed shelling of cross-border targets the next day, and parliament authorized the use of military force in Syria. Some Syrian soldiers are said to have been killed.

This is the most serious incident along Syria's borders since the revolution began in March 2011. It has potentially significant military implications, including escalation into a broader Turkish-Syrian conflict, creation of a de facto buffer zone in northern Syria, and further weakening of Bashar al-Assad's forces relative to the opposition Free Syrian Army (FSA). Damascus will likely back down and attempt to avoid a fight with Turkey, essentially leaving Ankara with the task of controlling escalation. Whatever the case, this development adds additional weight to arguments for a greater U.S. and allied role in ending the regime and the war in Syria.

BACKGROUND

Fighting between regime and FSA forces in Syria's northern Raqqa province has been escalating in recent weeks. The most dramatic event was the September 19 seizure of the border crossing at Tal Abyad. Regime forces have been unable to retake the crossing, and clashes continue in the province. The regime has relied heavily on airpower and artillery to strike FSA elements and areas where they are located, creating the potential for a serious border incident. The shell that hit Turkey and killed its citizens was probably an overshoot by regime units targeting Tal Abyad rather than a deliberate action against Akcakale.

SYRIA'S MILITARY OPTIONS

Syria has very few military options for responding to Turkey's action, especially in the short term. Regime ground forces in the area are limited to elements of one overstretched division, probably supported by shabbiha irregulars and local militias. Its ability to reinforce these elements is also quite limited. Regime combat formations are heavily committed to the internal war, and any reorientation for an external conflict would weaken their capacity in this vital contest. In addition, the area in question is at the outer range of Syria's surface-to-air missile systems, and even conventional antiaircraft artillery is probably limited in number and thinly deployed. Employing the Syrian air force against the Turks would be a major escalation, inviting a response from the more capable Turkish air force.

In light of these factors, the regime will likely eschew retaliation and instead focus on preventing further border incidents. According to Turkish sources, Damascus has admitted responsibility for the stray shelling and promised an investigation, and there has been no further cross-border fire by forces inside Syria.

TURKEY'S MILITARY OPTIONS

Ankara has built up its forces along the border since the June 22 downing of a Turkish reconnaissance aircraft by Syrian air defenses. In addition to deploying armor, artillery, and air-defense units, it has established rules of engagement allowing its forces to engage perceived threats from across the border. Turkey has indicated that its response to the October 3 incident was in accordance with these rules.

The previous buildup and parliament's authorization to conduct operations inside Syria puts Turkey in a relatively strong position militarily. Its actions pave the way for further military moves if necessary, including additional artillery strikes. Turkey could also decide to more aggressively enforce its rules of engagement for dealing with threats from Syria, limiting the ability of Assad's forces to operate close to the border.

For now, Ankara has made clear publicly that its actions are for deterrent purposes, and that it has no intention of going to war. And from a military standpoint, its approach has been restrained so far.

IMPLICATIONS

Limiting factors aside, the incident holds some potential for escalation. Turkey has already ratcheted up its political and diplomatic response, calling for NATO consultations, reportedly mobilizing forces, and threatening additional action if Syria conducts more attacks. And Assad's likely efforts to exercise greater control over his border forces may not succeed given the nature of the regime's fight with the opposition.

Although this is the most serious border clash thus far, incidents have also occurred on Syria's other frontiers, including deliberate shelling of areas inside Lebanon, exchanges of fire along the Jordanian border, and accidental firing into Israeli territory on the Golan Heights. As the regime intensifies its efforts to defeat the opposition and makes greater use of airpower and artillery, such incidents could grow in number and seriousness.

The key issue is what Ankara will do next. The shelling of Syrian targets for a second day indicates that Turkey wants to drive home the seriousness of any Syrian military action that reaches into its territory. And if reports of Turkish mobilization are true, they suggest broader intent, perhaps including enforcement of a buffer zone inside Syria. This would be a major psychological blow to the regime and its supporters and a significant boost for the rebels. Turkey's assertion of power across the border could transform what is now disputed territory in northern Syria into liberated territory; an opposition command could then operate from this area militarily and politically, and in relative safety.

Alternatively, regime fears of a broader Turkish response could create a de facto buffer zone even if the Turks do not explicitly establish one. That is, if Damascus becomes cautious about how it deploys and employs its forces close to the border, it would give the opposition an opportunity to strengthen and expand its hold on these areas with reduced risk.

If the Turkey-Syria crisis deepens, it could also place a greater burden on regime military resources already strained by the internal war. Any deployment of forces away from current centers of combat (e.g., Damascus and Aleppo) would weaken the regime's position in these areas and bolster the opposition. The very act of redeploying could present opportunities for armed rebels to attack exposed regime forces. In fact, a wider military crisis with Turkey could move the Syrian military closer to the breaking point -- the prospect of fighting Turkey, or even having to prepare and deploy for such a conflict, could prove too much for an already stretched and weakened force.

CONCLUSION

The latest incident is further evidence that the longer Syria's internal conflict continues, the more likely it is to become an external conflict that draws in neighbors. This risk -- together with the calamitous situation of the Syrian people, the drift toward more destructive civil war, and the threat of increasing radicalization among the rebels -- points to the need for direct or indirect intervention to topple the regime and the conflict.

Specifically, if Turkey takes a more active role by exerting control over the border area inside Syria, then the United States, its allies, and other countries interested in regional stability should all lend their support. This includes increased military, political, and humanitarian support to the opposition. For its part, Washington should provide assistance that helps defend and support areas in northern Syria where the FSA has a measure of control, and where free political and social institutions are emerging. These measures would help end the conflict, ensure direct and immediate aid for the Syrian people, and give the United States a chance to influence events after the regime falls.

Jeffrey White is a defense fellow at The Washington Institute. Soner Cagaptay is the Beyer Family fellow and director of the Turkish Research Program at the Institute. Andrew J. Tabler is a senior fellow in the Institute's Program on Arab Politics.