Russia, Turkey and Iran - the three main guarantors of a fragile, nationwide ceasefire in Syria - signed a deal on Thursday to set up so-called safe zones to mitigate the humanitarian crisis in the war-torn country.

The deal was announced during peace talks in the neutral state of Kazakhstan. Some of the Syrian opposition's delegation, which has opposed Iranian involvement, walked out in protest.

‘The agreement might good if it is implemented, but usually the Syrian regime and Iran say something and do something else,’ Syrian opposition representative Yahya al-Aridi told dpa.

‘If this agreement will be secure so that there will be no barrel bomb attacks on civilians, if it can stop the vicious killers who are murdering innocent people, it would be positive,’ al-Aridi said by phone.

The opposition's delegation believes that Iran cannot be considered a guarantor of the ceasefire because it is a ‘vicious killer like the regime,’ al-Aridi said.

The next round of peace talks in Kazakhstan is planned for mid-July.

Russian President Vladimir Putin suggested in talks on Wednesday with his Turkish counterpart Recep Tayyip Erdogan that military flights over such safe zones would most likely be prohibited.

Russia and Iran have been the main military backers of Syria's ruling regime, whereas Turkey has supported certain rebel groups seeking to overthrow Syrian President Bashar al-Assad.

 The three powers agree, however, that terrorist groups in Syria must be eradicated. The broad ceasefire does not include UN-designated terrorist groups, such as Islamic State.