Many of those injured suffered severe burns in Wednesday's air strike by a Syrian air force MiG fighter jet in the town of Aazaz near Aleppo, which killed more than 30 people instantly and left more than 200 injured.

Many of the wounded were taken across the border to hospitals in Turkey's southeastern city of Kilis, around 20 kilometres (12 miles) away, the Turkish official told AFP.

Some 15 of them succumbed to their wounds in hospital, the source said.

The Syrian Observatory for Human Rights said Wednesday that 31 people were killed in the aerial attack, the latest atrocity blamed on the regime of President Bashar al-Assad, and that the toll was expected to rise.

The number of Syrians crossing into Turkey has dramatically increased since the Syrian army ramped up its offensive against rebels in cities close to the Turkish border, particularly around Aleppo.

Turkey is sheltering around 62,000 refugees in camps in the south of the country and also providing sanctuary to Syrian military defectors in a separate camp near the border, where security is tighter.