June 20 (Reuters) - Iran's top joint military command, Khatam al-Anbiya Central Headquarters, said on Saturday that the Strait of Hormuz would be closed to vessel traffic, citing alleged violations of a ceasefire agreement by the U.S. and Israel, Iran's Mehr state news agency reported. It said that the closure was the "first step" in response to what it described as breaches of commitments and warned that further measures would be taken if "aggression" continued.