A top United Nations official is warning that an all-out Syrian government ground offensive against Idlib province—the last major rebel-held territory in Syria—could lead to the worst loss of life in the 21st century.

Mark Lowcock: “There needs to be ways of dealing with this problem that don’t turn the next few months in Idlib into the worst humanitarian catastrophe, with the biggest loss of life, of the 21st century. You know, we had the tsunami in 2004, which killed a quarter-million people, roughly; we had the atrocious famine in Somalia in 2011, which killed another quarter-million people. We must—we must—it’s not acceptable to have huge loss of life in Idlib over the next period.”