Turkey's military launched a retaliatory strike after Syria fired a mortar bomb into countryside in Turkey's southern province of Hatay.

It was the sixth consecutive day of Turkish retaliation against bombardment from the Syrian side of the border, where President Bashar al-Assad's forces are battling rebels.

The exchanges are the most serious cross-border violence in Syria's revolt against Mr Assad, which began in March last year.

The latest mortar round from Syria landed 150-200 metres within Turkey's border in the district of Hacipasa at about 3pm (1pm Irish time), an official said.

Turkey's armed forces have bolstered their presence along the 900km border with Syria in recent days.

Syrian rebel sources in the country’s Raqqa province, bordering the Turkish town of Akcakale where Syrian shelling killed five civilians last Wednesday, said they had seen five Turkish army trucks full of soldiers, patrolling the Turkish side of the border.