DUBAI, United Arab Emirates (AP) — A U.S. airstrike on an important oil port held by Yemen's Houthi rebels killed more than 70 people and wounded many others, the Iranian-backed rebel group said Friday, marking a major escalation in the military campaign President Donald Trump launched against the faction last month. The overnight strike on the Ras Isa port sent massive fireballs billowing skyward and turned tanker trucks into burning wrecks. It was the first American attack on a Houthi-controlled oil facility since the U.S. began its new bombing campaign. It also came just before the resumption of negotiations in…