The UN children's agency UNICEF has issued a mostly blank statement to express their outrage at the situation in Syria's Eastern Ghouta.
It comes amid reports that scores of civilians have been killed in strikes targeting the rebel-held enclave in recent days.
Eastern Ghouta - which is around 15 kilometres from Damascus city centre - has been besieged by the Syrian army since 2013, and it is one of the few areas in the country still under rebel control.
The last several weeks have seen the area targeted by Russia-backed Syrian government forces.
In a statement issued yesterday, the UN said it had received reports of more than 100 people killed, including 13 children, since Monday.
Monitoring groups and rescue teams on the ground put the number even higher, with the Syrian Observatory for Human Rights saying 250 civilians were killed over a 48-hour period.
The group said that number marked the highest two-day death toll in the area since a deadly chemical attack in 2013.
The Syria Civil Defence search & rescue group - also known as the White Helmets - have been posting videos of its operations in Eastern Ghouta.
Direct hit on the civilians and @SyriaCivilDefe volunteers while they are helping the injured people, this is the double tab strategy. #Haza city #EasternGhouta. #SaveGhouta pic.twitter.com/Ua4oGczkrY
— The White Helmets (@SyriaCivilDef) February 20, 2018
UNICEF, meanwhile, issued a 'blank statement'.
In a brief note, UNICEF said: "We no longer have the words to describe children’s suffering and our outrage.
"Do those inflicting the suffering still have words to justify their barbaric acts?"
UN Secretary General Antonio Guterres said he is 'deeply alarmed' by the escalating situation in Eastern Ghouta and 'its devastating impact on civilians'.
In a statement, a spokesperson for Mr Guterres said: "Nearly 400,000 people in Eastern Ghouta have been subjected to airstrikes, shelling and bombardment. As a result of the siege of the area by the Syrian Government forces, residents of this area are living under extreme conditions, including malnutrition.
"The Secretary-General urges all stakeholders to ensure that basic principles of international humanitarian law are adhered to, including unhindered humanitarian access, unconditional medical evacuations, and the protection of civilians and civilian infrastructure."
The conflict in Syria has seen more than 300,000 people killed and millions more displaced since it began in early 2011.