The envoy added that the United Nations would not give up seeking a full 30-day ceasefire, as recently mandated by the Security Council. So any type of feeling that the U.N.is frustrated: "Forget it", he said.
Rebel sources could not immediately be reached for comment on Friday.
"Otherwise, [the Eastern Ghouta assault] becomes a copycat of Aleppo", he said.
Russian Federation and Turkey said they were able to arrange the evacuation of some 700 civilians from Eastern Ghouta, but outside observers said they could not confirm the evacuation took place, and the Turkish government conceded the civilians were not brought to Turkey for medical treatment as President Recep Tayyip Erdogan wanted.
"It is a question [of] life and death - if ever there was a question of life and death - we need a 30-day cessation of hostilities in Syria as the Security Council demands", said Mr Laerke, spokesman of the UN Office for the Coordination of Humanitarian Assistance (OCHA).
Syrian child Khaled al Ghorani lies at a clinic after he had his hand amputated in Kafar Batna in the Syrian opposition enclave of eastern Ghouta on March 1, 2018 following reported air strikes by Syrian regime forces.
"My thoughts often turn to that beloved and martyred Syria where the war has intensified, especially in eastern Ghouta", he said February 25 after praying the Angelus with people gathered in St. Peter Square.
Since the passage of this UN Security Council resolution, there continue to be reports of attacks on civilians and civilian objects in the besieged enclave of Eastern Ghouta, and no humanitarian convoys have had access.
Syrian government forces have besieged Eastern Ghouta for more than four years.
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"We may now be able to go to Eastern Ghouta in the next few days", said Jan Egeland, head of the UN's humanitarian taskforce for Syria.
The accusations come on the third and possibly last day of a Russia-ordered "humanitarian pause" in the fighting in the area, known as eastern Ghouta, but no civilians have used the lull to leave the rebel-held suburbs.
It posted photos showing the couple holding Pakistani ID cards and sitting inside a vehicle that appeared to belong to the Syrian Arab Red Crescent.
Elsewhere in Syria, a convoy of 28 trucks carrying aid entered the northern Kurdish enclave of Afrin, where Turkish troops have been on the offensive since January 20 against Syrian Kurdish fighters.
Air strikes have continued to take place across the suburb, despite Russian Foreign Minister Sergei Lavrov's announcement of a daily five-hour ceasefire to be implemented in the enclave to allow a safe route for the wounded to be evacuated and civilians to escape.
"We can not see a copycat of Aleppo taking place", De Mistura said.
Humanitarian groups are unable to deliver vital supplies into Eastern Ghouta in the short pause in fighting offered by Russian Federation, the United Nations has said.
As dozens of aid trucks remained unable to enter the enclave, the UN Human Rights Council postponed voting on a British resolution condemning the crisis in Eastern Ghouta, after member states failed to agree on a final text. The situation worsened when the Islamic State terrorist group began interfering in the country in 2014.