Seven years of conflict in Syria have left about 511,000 people dead, according to the Syrian Observatory for Human Rights. The Britain-based monitoring group, which relies on an extensive network of sources on the ground across Syria, said about 85 percent of the dead since March 15, 2011 had been killed by regime forces and their allies. The conflict, which will enter its eighth year on Thursday, is taking a devastating toll on civilians, including in the ongoing regime assault on the rebel enclave of Eastern Ghouta, near Damascus. Meanwhile, UNICEF said children are at more risk than ever in Syrias war. The UN childrens agency reported a 50 percent increase in the number of children killed in the conflict last year compared to the previous year. "In 2017, extreme and indiscriminate violence killed the highest ever number of children -- 50 per cent more than 2016," it said, adding that 2018 was off to an even worse start. More than 200 children have been killed in bombardment of Eastern Ghouta by Syrian regime and allied forces since February, according to the Observatory. The monitoring group says children account for around a fifth of all civilian victims of the assault. The UN agency quoted a child from southern Syria named Sami, who is now a refugee in Jordan. "I went outside to play in the snow with my cousins. A bomb hit. I saw my cousins hands flying in front of me. I lost both my legs," he said. Disabled children "face a very real risk of being neglected and stigmatized as the unrelenting conflict continues," said UNICEF regional director Geert Cappelaere. According to the UN agency, an estimated 3.3 million children are exposed to explosive hazards across the war-torn country. Dozens of schools were hit in 2017 alone.