ANTAKYA, Turkey - Syrian helicopter gunships reportedly bombarded a strategic town in northern Syria overnight and tanks moved close to the commercial hub and its largest city Aleppo, rebel fighters said on Friday.
Meanwhile, anti-regime groups reported what one called a "hideous massacre" in Douma, outside of Damascus, and distributed a video and photograph purportedly showing the aftermath of a killing that left more than 50 dead, including women and children. Journalists do not operate freely in Syria so there was no way of confirming the report.
A senior rebel officer said around 170 Syrian tanks had assembled at an infantry school near the village of Musalmieh northeast of the city of Aleppo, just 19 miles from the Turkish border but were keeping well clear of new Turkish air defenses installed to curb Syrian action near its frontiers.
"They're either preparing to move to the border to counter the Turkish deployment or attack the rebellious (Syrian) towns and villages in and around the border zone north of Aleppo," General Mustafa al-Sheikh, head of the Higher Military Council, a grouping of senior officers who defected from Assad's forces, told Reuters by telephone from the border.
Omar Abdallah, an activist in Idlib coordinating with the Free Syrian Army said: "After taking hits in rural Aleppo and Idlib, the army is re-grouping ... There is speculation that these forces intend to ring Aleppo starting July 1."
Turkish commanders inspected the missile batteries deployed on the border region on Thursday following Syria's shooting down of a Turkish warplane a week ago, which has sharply raised tensions between the two nations.
Meantime, Syrians in the besieged city of Douma wrapped mangled and bloodied corpses in white burial shrouds early on Friday, according to video posted online.
"A massacre has been committed in the city of Douma, killing more than 50 in this bloody day, where Assad mafias and death squads launch aggressive attacks, bombardment of the city, and executions," U.S.-based anti-Assad Syrian Expatriates said a statement.
Douma is predominantly Sunni community that has become as a focus of resistance to the Assad government.
The group gave details for the killings of 10 members of the same family, including four chidren, their mothers and grandmother. More than 200 were wounded, the group said.
The British-based Syrian Observatory for Human Rights said 190 people, including 125 civilians, were killed on Thursday throughout the country.
The United States, Britain and France have said that Assad is responsible for the violence, which the United Nations estimates has killed at least 10,000 people, and is no longer fit to govern. Russia and China, however, reject what they describe as Western calls for "regime change."
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 on Friday he was "optimistic" that crisis talks in Geneva on Saturday would produce an acceptable outcome, which has so far proved elusive.
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.
Recently, there were clashes close to the border between Syrian forces and rebels. Last weekend, Damascus said "terrorists" infiltrating from Turkey were killed and there have been reports of Syrian forces shooting into camps for refugees in Turkey.
Turkey, sheltering some 34,000 Syrian refugees and providing bases for the rebel Free Syria Army (FSA), is in the forefront of the efforts to bring down Assad.
Syrian tanks mass
Rebel sources in Turkey's Hatay region said Assad's helicopters attacked Saraqeb, a strategic town deep in Idlib province, but kept away from the area directly along the Turkish border in the rural regions of Idlib and Aleppo provinces.
Neither Turkey, which fears a local clash escalating into a regional sectarian conflagration, nor Syria, has any interest in a confrontation on their shared border.
Ankara, which has the second biggest army in NATO, called an emergency NATO meeting after its warplane was shot down.
Turkey has in the past talked about creating a humanitarian corridor on Syrian territory if refugee flows became dangerously unmanageable or the scale of killing in Syria became intolerable. But it had always said this would require international endorsement.
"NATO just doesn't look like it's in the mood," David Hartwell, Middle East analyst, IHS Jane's, said. "What you might get is the Turks forcing a de facto no-fly zone."
Erdogan announced earlier this week that he had issued new rules of engagement to his border troops and said any Syrian military elements approaching Turkish borders and deemed a threat would be treated as a target. But he failed, perhaps deliberately, to specify how close Syrian forces could come to the border before becoming vulnerable.
"The Syrians might accept a very narrow zone along the border. Syria will remain very reluctant to get involved in any conflict with Turkey. They would be up against a very serious military foe," Malcolm Chalmers, research director at Britain's Royal United Services Institute, said.
The world has been accused by Syrian opposition activists of inertia over the bloodshed. Diplomacy has failed to produce agreement between Western powers, backing the opposition, and Russia, which has used its U.N. veto to block Western and Sunni Arab moves to drive Assad from power.
Reuters and msnbc.com's F. Brinley Bruton contributed to this report.
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