UN Secretary General Ban Ki-moon reiterated Sunday evening the call for both sides in the Syrian conflict to halt the escalating violence immediately and unconditionally.

Ban, who has just started a visit to Croatia as part of a week-long Bankan tour, said the deteriorating situation in Syria could have a serious spillover on the entire Middle East and the Mediterranean basin.

He made the press remarks in Brijuni Island, after his talks with Croatian Prime Minister Zoran Milanovic.

"The Syrian government has manifestly failed to protect its civilians, and the international community has a collective responsibility to live up to the UN charter and act on its principles," Croatia radio quoted Ban as saying.

He was commenting on the Russian-Chinese veto that blocked a UN Security Council resolution on Syria three days ago.

Meanwhile, the UN chief praised as "a constructive sign" the UN Security Council resolution 2059 on Friday to allow a "final" 30-day mandate extension to the UN Supervision Mission in Syria.

He noted that he was sending to Syria the UN peacekeeping chief Herve Ladsous, of France, as well as chief UN military adviser General Babacar Gaye to assess the situation there; Gaye, is to lead the UN Supervision Mission in Syria (UNSMIS) in this critical phase.

Affirming that "the UN remains actively engaged and fully mobilized," Ban said he was "deeply distressed by the rising death toll and the number of people forced to flee their homes" as troops clashed with rebels in Syria's second city of Aleppo yesterday.

As for his Balkan tour, Ban said it aimed to identify the problems of the region and review the roles being played by the UN agencies to assist the countries in the region over the last two decades.

He called for scaling up the efforts to end the differences between Serbia and Kosovo through negotiations.

Ban started the tour with a visit to Slovenia on Friday before proceeding to Croatia, Serbia, Kosovo, Macedonia and Bosia and Herzegovina; he leads a UN delegation including Deputy Secretary General for Political Affairs Jeffery Feltman and the Croat delegate to in the UN Ivan Simunovic.