UN Secretary General Ban Ki-moon warned Monday of a "dangerous' fallout from spiralling violence along the Syrian-Turkish border, as regime troops shelled rebel bastions across Syria leaving dozens dead.

"The escalation of the conflict along the Syrian-Turkish border and the impact of the crisis on Lebanon are extremely dangerous," Ban said at the opening of the World Forum for Democracy in Strasbourg, France.

The armed uprising in Syria has increasingly sparked violence on the country's border with NATO member Turkey, with the Turkish military returning fire on Sunday after a shell launched from Syria struck the border village of Akcakale.

There were no casualties in Sunday's incident, but last Wednesday five civilians were killed in the village by shelling from Syria.

Since Wednesday, the Turkish military has responded in kind whenever Syrian ordnance has breached its territory, inflaming tensions between the former allies and leading to fears of a broader conflict.

Turkey's parliament on Thursday gave the government the green light to use military force against Syria if necessary.

The UN Security Council has strongly condemned cross-border attacks by Syria and called for restraint between the two neighbours whose ties have nosedived, with Ankara supporting the rebels fighting President Bashar al-Assad's regime.

Shelling from Syria into Lebanon and cross-border shootings, meanwhile, have become regular occurrences, while residents of Lebanon's frontier region accuse Syria's army of carrying out frequent incursions and kidnapping refugees.

The UN chief also raised concerns about arms supplies to both Assad's regime and rebel forces.

"I am deeply concerned by the continued flow of arms to both the Syrian government and opposition forces. I urge again those countries providing arms to stop doing so," he said.

"Militarisation only aggravates the situation," he said. "I am calling on all concerned to abandon the use of violence, and move toward a political solution. That is the only way out of the crisis."

Inside Syria, regime forces brought in the artillery early Monday to shell a string of rebel strongholds that left at least 23 people dead, the Syrian Observatory for Human Rights said.

Most of the deaths occurred when the army launched intensive pre-dawn assaults on the town of Karak al-Sharqi in the southern province of Daraa and on pockets of rebel resistance in Aleppo, Syria's commercial capital, the Britain-based watchdog said.

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