On Saturday, the UN Security Council unanimously approved a resolution demanding a 30-day ceasefire across Syria
The UN Secretary General has called for the immediate implementation of a ceasefire in Syria, saying it is "high time to end the hell on earth" in Eastern Ghouta.
The comments by António Guterres come two days after the the UN Security Council passed a resolution demanding a 30-day humanitarian ceasefire in Syria.
The vote followed a week that brought reports of hundreds of civilian deaths amid relentless airstrikes against the rebel-held Eastern Ghouta enclave.
Mr Guterres told the UN Human Rights Council in Geneva that he expected the Security Council resolution to be "immediately implemented and sustained" - stressing that it is only meaningful if implemented.
Security Council resolutions are only meaningful if implemented. Eastern Ghouta cannot wait. High time to end this hell on earth. pic.twitter.com/KzXJtjtNcm— António Guterres (@antonioguterres) February 26, 2018
Meanwhile, Zeid Ra'ad Al Hussein, the UN's human rights chief, argued: "Eastern Ghouta, the other besieged areas in Syria, Ituri and the Kasais in the (Democratic Republic of Congo), Taiz in Yemen, Burundi, Northern Rakhine in Myanmar have become some of the most prolific slaughterhouses of humans in recent times because not enough was done, early and collectively, to prevent the rising horrors."
Mr Zeid said Security Council members who had vetoed action in conflict zones bear a "responsibility for the continuation of so much pain", adding: "It is time, for the love of mercy, that China, Russia and the United States end the pernicious use of that veto."
He urged caution in relation to the Security Council resolution, saying: "The resolution must be viewed against a backdrop of seven years of failure to stop the violence, seven years of unremitting and frightful mass killing."
Despite the increased international pressure for a ceasefire, there have been continuing reports of civilian casualties in Eastern Ghouta over the weekend.
According to the Syrian Observatory for Human Rights monitoring group, nine civilians - including three children - were killed in an airstrike overnight in Douma city.
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.
The conflict in Syria has seen more than 300,000 people killed and millions more displaced since it began in early 2011.
Additional reporting by IRN