UNITED NATIONS - The United States told the United Nations on Wednesday that the killing of Iranian commander Qasem Soleimani last week was self-defense and vowed to take additional action "as necessary" in the Middle East to protect U.S. personnel and interests.Iran retaliated on Wednesday for Soleimani's death by firing missiles at military facilities housing U.S. troops in Iraq. U.S. President Donald Trump said no Americans were hurt, soothing fears that Soleimani's death and the Iranian response could spark a wider conflict in the Middle East. In a letter to the U.N. Security Council, US Ambassador Kelly Craft said the United States also stands "ready to engage without preconditions in serious negotiations with Iran, with the goal of preventing further endangerment of international peace and security or escalation by the Iranian regime."The killing of Soleimani in Baghdad on Friday was justified under Article 51 of the U.N. Charter, wrote Craft in the letter seen by Reuters, adding "the United States is prepared to take additional actions in the region as necessary to continue to protect U.S. personnel and interests."Under Article 51, countries are required to "immediately report" to the 15-member Security Council any measures taken in exercising the right of self-defense. The United States used Article 51 to justify taking action in Syria against Islamic State militants in 2014.Craft said Soleimani's death and U.S. airstrikes in Iraq and Syria on Dec. 29 against an Iran-backed militia group were "in response to an escalating series of armed attacks in recent months by the Islamic Republic of Iran and Iran-supported militias on U.S. forces and interests in the Middle East."She said the aim was to deter Iran from conducting or supporting attacks and degrade its ability to conduct attacks.Iran also justified its action under Article 51 of the U.N. Charter in a letter to the U.N. Security Council on Wednesday. The U.S. letter to the U.N. Security Council arrived after Iran's letter, diplomats said.Iran's U.N. Ambassador Majid Takht Ravanchi wrote that Tehran "does not seek escalation or war" after exercising its right to self-defense by taking a "measured and proportionate military response targeting an American air base in Iraq.""The operation was precise and targeted military objectives thus leaving no collateral damage to civilians and civilian assets in the area," Ravanchi wrote."Seriously warning about any further military adventurism against it, Iran declares that it is determined to continue to, vigorously and in accordance with applicable international law, defend its people, sovereignty, unity and territorial integrity against any aggression," he said.Iran had full respect for the sovereignty of Iraq, he added.