Helicopter gunships bombarded a strategic town in northern Syria overnight and tanks moved close to the commercial hub of Aleppo, rebels have said.
They said the Syrian forces kept well clear of new Turkish air defences installed to curb Syrian action near its frontiers.
The Turkish deployments, a graphic warning to President Bashar al-Assad, coincide with rising violence across Syria and increasingly urgent international efforts to forge a peace deal as the nation slips into full-blown war.
As the Turkish-Syrian dimension ratcheted up further pressure, peace envoy Kofi Annan said today he was "optimistic" that crisis talks in Geneva tomorrow would produce an acceptable outcome, which has so far proved elusive.
Senior officials holding preparatory talks in Geneva today failed to overcome differences on Mr Annan's plan for a political transition.
Western diplomats said Russia was pressing for changes to the text.
Russian diplomats said the work continued but they would not "impose" a solution on Syria.
Russian Foreign Minister Sergei Lavrov said after meeting US Secretary of State Hillary Clinton over dinner in St Petersburg that he saw a "very good chance" of finding common ground when the group of foreign ministers met Mr Annan in Geneva.
A senior US State Department official said, however, that differences remained between Washington and Moscow on Syria.
Of the chances of an accord when the ministers met again in Geneva, the official said: "We may get there tomorrow. We may not."
Regional analysts said that while neither Turkey nor its NATO allies appeared to have any appetite to enforce a formal no-fly zone over Syrian territory, Prime Minister Tayyip Erdogan had made it clear Assad would be risking what he called the “wrath” of Turkey if its aircraft strayed close to its borders.
Mr Erdogan told a rally in the eastern city of Erzurum, broadcast by Turkish television: "We will not hesitate to teach a lesson to those who aim heavy weapons at their own people and at neighbouring countries."
