Turkey returned fire across the Syrian border after a mortar shell - believed to be fired by Syrian troops and aimed at opposition groups on the border -landed in southern Turkey on Saturday morning.

"The Syrian mortar shell landed close to a rural area near the Guvecci village of Yayladagi town of Hatay province. Turkey retaliated against Syria by firing four mortar shells on Syria," said the statement issued by the Hatay governor's office on its website.

The latest shelling comes a day after Turkey called on Syria not to test Turkey's "limits and determination" and insisted that the country "was not bluffing" with its warnings.

Turks hold banners that read "no to war" during a protest in Ankara on Friday. Turkey's Prime Minister Recep Erdogan again warned Syria it would pay a big price for further attacks, two days after a deadly cross-border shelling. [Photo/Agencies]

The mortar shell landed in a rural area near the village of Guvecci, early on Saturday morning, just minutes after intense fighting broke out between the forces of Syrian President Bashar Assad's government and the rebels in the village of Harabjoz, in Syria's Idlib province near the border, the private Dogan news agency reported.

No one was hurt by the mortar shell, which landed some 500 meters outside of the village. But Turkish artillery based at an army battalion near Guvecci immediately responded with "counter-fire", the state-run Anadolu Agency said.

Villagers rushed out of their homes and gathered at a safer point in the village, away from the border area.

The latest tensions with Syria began Wednesday when a Syrian shell hit a home at a Turkish border town, killing two women and three children.

The shelling sparked unprecedented artillery strikes by Turkey.

Turkey's parliament on Thursday also voted to allow cross border military operations in Syria, further raising tensions between the neighbors that were once close allies.

On Friday, a Syrian mortar shell fell at a spot about 50 meters from the border in Hatay's Asagipulluyazi village. The Turkish army "fired back at targets" within Syria, but did not cause any casualties, said Hatay Governor Mehmet Celalettin Lekesiz.

The United States sided with Turkey on Friday, condemning what White House spokesman Josh Earnest called the "aggressive actions of the Syrians". Earnest said Turkey's response was appropriate and that the US stands by Turkey, a NATO ally.

Saturday's shelling came as both sides appeared to be trying to defuse the situation. A Turkish Foreign Ministry official said on Friday that Syria has pulled tanks and other military equipment away from the border.

Turkey should be prepared for war if it wants to have peace, Turkish Prime Minister Recep Tayyip Erdogan said in Istanbul on Friday.

Addressing a gathering of more than 5,000 people, Erdogan said, "The saying goes: 'prepare for war if you wish for peace' We are not war-lovers, but we are not far from war either."

China urged all sides to exercise restraint and refrain from taking further actions that will escalate tensions, according to Foreign Ministry spokesman Hong Lei on Thursday.

The situation is still "under control" and the possibility of the tension turning into a regional conflict is bleak, according to He Wenping, a researcher on North Africa and West Asia studies at the Chinese Academy of Social Sciences, as the Syrian side does not want to further provoke Turkey and had already apologized for the mortar attack.

The start of the current tension, which was triggered more by accident, is less intense than when Syria shot down a Turkish reconnaissance jet in June, which prompted Ankara to immediately increase its military presence along its border with Syria and call a meeting of NATO's North Atlantic Council, she said.

"NATO does not want to intervene militarily in the current situation this time, though it said it stood by its ally, not to mention the US, whose presidential campaign is reaching a critical stage at the moment," she said.

AP-Xinhua-China Daily