UNITED NATIONS — Yemen risks being dragged further into the military escalation in the Middle East that keeps intensifying and could spiral out of control, the U.N. special envoy for the Arab world’s poorest nation said Tuesday. Hans Grundberg told the U.N. Security Council that regrettably Yemen is part of the escalation — and he warned that repeated attacks on international shipping by its Houthi rebels “have significantly increased the risk of an environment disaster” in the Red Sea. Both