HACIPASA, Turkey: Turkey's military chief of staff said on Wednesday his troops would respond with greater force if bombardments from Syria keep hitting Turkish territory.
Several mortar bombs landed outside the Syrian border town of Azmarin and heavy machinegun fire could be heard from the Turkish side as clashes between the Syrian army and rebels intensified along the border.
Plumes of smoke rose into the sky and cries of "God is Greatest" rang out between the bursts of gunfire.
Turkey's armed forces have bolstered their presence along the 900-km (560-mile) border and have been responding over the past week to gunfire and shelling coming across from northern Syria, where President Bashar al-Assad's forces have been battling rebels who control swathes of territory.
"We responded but if it continues we will respond with greater force," state television TRT quoted Turkey's Chief of Staff, General Necdet Ozel, as saying.
NATO Secretary-General Anders Fogh Rasmussen said on Tuesday the military alliance had plans in place to defend Turkey. He gave no further details but a senior U.S. defence official said NATO would likely react if Turkey made a request for assistance.
It is not clear whether the shells that have hit Turkish territory were aimed to strike there or were due to Syrian troops overshooting as they attacked rebel positions. Turkey has provided sanctuary for rebel officers and fighters.
General Ozel visited the family of five civilians killed last week by a Syrian mortar strike in the town of Akcakale before flying by helicopter to a military base further east along the frontier.
Turkish Prime Minister Tayyip Erdogan, once an ally of Assad but now one of his harshest critics, said in Istanbul that Turkey's objective was to secure peace and stability in the region, not to interfere in Syria's domestic politics.
"We warned Assad. We reminded him of the reforms he should introduce...unfortunately the Assad regime didn't keep its promises to the world and its own people," Erdogan said.
"Nobody should or can expect us to remain silent in the face of the violent oppression of people's rightful demands."
The Syrian Observatory for Human Rights said 70 people had been killed across the country on Wednesday, including six rebels in the strategic town of Maarat al-Nuaman, on the north-south highway linking Aleppo to the capital Damascus.
Activists and rebels had said on Tuesday that the insurgents seized control of the town after a 48-hour battle but clashes continued in and around Maarat al-Nuaman on Wednesday.
Rebels said they halted an army push to retake the town on Wednesday in heavy fighting that killed 30 rebels and scores of government soldiers.
"It was stopped at a heavy cost," Abu Musab Taha, a rebel commander in the area told Reuters.
Anas Othman, a resident of Maarat al-Numaan, said the town "is being destroyed" by air strikes and army artillery.
Opposition sources said the fall of Maarat al-Numaan has further weakened the army supply lines to Aleppo, where urban warfare has been raging for two months.
Scores of Syrian civilians, many of them women with screaming children clinging to their necks, crossed a narrow river marking the border with Turkey as they fled the fighting in Azmarin and surrounding villages.
Residents from the Turkish village of Hacipasa helped pull them across in small metal boats.
"The firing started getting intense last night. Some people have been killed, some are lying wounded on the road," said a 55-year old woman, Mune, who fled Azmarin and sat with several adults and about 20 children outside a house in Hacipasa.
"People want to escape but they can't. Many have settled in a field outside the town and are trying to come," she said, describing how she had helped ferry the children over another point in the river in a metal bowl used for wheat.
Doctors and volunteers set up makeshift first aid points on both sides of the frontier. A Turkish ambulance and several minibuses and cars waited to take the more seriously wounded to the main city of Antakya or district hospitals.
"Don't take me across, take me back. I want to return and fight," said one man being carried on a stretcher, his T-shirt stained with blood.
A sharp rise in casualties in Syria in the past month indicates the growing intensity of the conflict, which spiralled from peaceful protests against Assad's rule in March 2011 into a full-scale civil war.
The Syrian government said on Wednesday that an appeal by U.N. Secretary General Ban Ki-moon for a ceasefire was only acceptable if the rebel forces agreed to abide by it too.
Foreign Ministry spokesman Jihad Makdissi said two previous attempts at a ceasefire had broken down when the rebels carried out attacks. U.N. observers at the time said government forces had also violated the truce.
Ban had asked for a unilateral truce, Makdissi said. Damascus replied that the goal of any truce was to prepare the ground for dialogue, not to seek military advantage.
"We requested the Secretary General to send delegates to the relevant countries, specifically Saudi Arabia, Qatar and Turkey, because those are the countries that finance, shelter, train and arm these armed groups, so that they can show their commitment to stopping these acts," he said.
As well as the combat along the northern border, government and rebel forces are still fighting over districts of Homs in the west, Aleppo in the north, and other towns and cities.
Damascus has been hit by a series of bombings of strategic buildings that have brought the war close to Assad's seat of power but the rebels have been unable to keep a foothold in the center, although clashes are frequent in the suburbs.
The government has made heavy use of airpower and artillery to halt rebel advances, flattening parts of city neighbourhoods.