The U.N. secretary-general has urged leaders to "exercise maximum restraint" following the U.S. airstrike that killed Iran's top military commander. Antonio Guterres stressed that "the world cannot afford another war in the Gulf," U.N. deputy spokesman Farhan Haq said in a statement. Guterres "is deeply concerned with the recent escalation" in the region, Haq said. The airstrike that killed Gen. Qassem Soleimani near the Baghdad airport marked a major escalation in the conflict between the United States and Iran. U.S. President Donald Trump says Soleimani was "plotting to kill" many Americans. Iran's supreme leader has vowed "harsh retaliation."