Turkish Prime Minister Tayyip Erdogan, once a firm ally of Assad, said he was considering setting up a buffer zone along the border with Syria. Ankara might then withdraw its ambassador once its nationals had returned home.
"A buffer zone, a security zone, are things being studied," he told reporters in Ankara, but said other ideas were also under consideration. "It would be wrong to look at it from only one perspective."
This is something that I've been expecting since the summer when Turkey issued an ultimatum to Assad to stop killing civilians. At the time, many people said Turkey couldn't pull off an intervention. Whether or not that was true at the time, Turkey has had over 6 months to prepare for such an intervention.
While not a decisive action, it is more likely that it can be done without appearing overtly anti-Assad. It puts Assad in a dilemma: allow sanctuaries for the Free Syria Army to be established on Syrian soil or challenge the Turkish forces and perhaps invite NATO aerial intervention or even a full Turkish invasion that drives on Damascus after Assad throws the first punch.
UPDATE: I didn't know if I should draw too much of a conclusion from the line "once its nationals had returned home," but Strategypage writes that the Turks told their people to leave Syria.
Now the question may be what international body is sufficient to green light the sort-of invasion. The UN Security Council won't because China and/or Russia will veto that route. Would the General Assembly provide enough cover for Turkey to move? Would NATO approve as in 1999 for Kosovo? Would an Arab League request (well, we twisted it enough to get a UNSC resolution that we also twisted) be sufficient, as it was for Libya last year? Is there some other body that Turkey might consult the way we got the OAS to ask us to deal with Grenada in 1983?
If Turkey has decided to go in, they'll find some body to provide the diplomatic cover, secure in the knowledge that a UN Security Council veto by America, France, or Britain will prevent a condemnation of Turkey in the Security Council (if that type of resolution could get even the votes to pass without a veto).