Turkey is worried about a potential flood of refugees over the border in the event of a full-on civil war, and is also starting to experience a swing in public opinion against Assad and some protests in support of the rebels stirred up by the Muslim Brotherhood. They've been front-and-centre in condemning the Syrian authorities' crackdown since it started, and warned Assad back in May that Turkey would intervene if there was anything like a repeat of the 1976 Hama massacre.

Seems to me they've done a U-turn like pretty much every other country in Europe - because the Syrian government wasn't killing people before and it is now.