BAGHDAD — Saudi Arabia cut diplomatic ties with Iran on Sunday and gave all Iranian diplomats 48 hours to leave the kingdom, as escalating tensions over the execution of an outspoken Shiite cleric in Saudi Arabia marked a new low in relations between the two Middle Eastern powers. The surprise move, announced in a televised news conference by Adel al-Jubeir, the Saudi foreign minister, followed harsh criticism by Iranian leaders of the Saudi execution of Sheikh Nimr al-Nimr and the storming of the Saudi Embassy in Tehran by protestors in response. Mr. Jubeir said that the kingdom would not allow...