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GENEVA, April 18 (Xinhua) -- The Syrian opposition the High Negotiations Committee (HNC) on Monday evening issued a statement, saying that they have asked UN Special Envoy for Syria Staffan de Mistura to place the talks "on a brief hold".

Meanwhile, the statement re-confirmed that the HNC will remain in Geneva for "serious talks".

De Mistura has told the press on Monday that the HNC is intending to suspend their formal presence to the ongoing peace talks in the UN headquarters of the Palace des Nations, but will remain staying in Geneva for technical discussions.

"I heard intention of HNC to postpone their formal participation in Palais in negotiations due to ground realities,"he said during a press briefing here on Monday evening.

However, the UN special envoy said that he will continue discussions and consultations with both sides, since "proximity talks are very flexible".

He added that he will review the situation again later on Friday.

Earlier in the day, the head of the main Syrian opposition delegation, Riad Hijab, said in a series of comments posted on Twitter that the Syrian government and its allies have used the talks as a "pretext" for waging their military campaign, and keeping up its siege of civilian areas.

According to the HNC, to suspend their "formal presence" to the talks is one way for them to express concern and frustration over humanitarian and security situation.

During Monday evening's press briefing, de Mistura said that no one can deny the fighting taking place in some areas particularly in Aleppo and this is becoming "worrisome", but truce is still holding "in many areas".

"Truce is holding in many areas, but increase in fighting is worrisome, humanitarian access is going too slowly," he said, adding that this will be brought into the discussion of the next meeting of the International Syrian Support Group meeting on Tuesday and hopefully "we may have tomorrow some convoys moving".

The UN envoy stressed that on political track, "we should not expect that after five years of conflict a political transition by miracle in one week is solved".

According to him, so far everyone in the talks have agreed that political transition is the core point of the agenda, and he will still make efforts to narrow the gap between both sides.

The second phase of the Intra-Syrian talks kicked off on April 13 in Geneva, entered into its second week Monday when de Mistura is scheduled to meet respectively the government and the opposition delegation.

The latter sent a sharply-reduced delegation, from the usual at least 10 people to only three, to meet with the UN mediator on Monday afternoon.

The government delegation is still scheduled to meet the UN envoy again on Wednesday.