BIG: US forces exit Iraq by tomorrow after 20+ years, ending a presence where 4,500 Americans died.

Iran-backed groups call it "a historic victory" and "a crushing defeat for the American project."

Iraqi security officials warn the withdrawal is premature.

The last US soldier killed in Iraq died in July during a drone detonation near Erbil.

Seven of 18 US service members killed in this year's Iran war died in Iraq.

Source: Reuters