Washington: The US has said it is "ready to engage without preconditions in serious negotiations" with Iran following the countries' exchange of hostilities.
In a letter to the UN, the US justified the killing of Iranian General Qasem Soleimani as an act of self-defence, the BBC reported on Thursday.
Iran has retaliated by firing missiles at air bases housing US forces in Iraq causing no casualties. It also told the UN it was an act of self-defence.
Gen. Soleimani was widely held as being Iran's second most senior official.
As head of the Revolutionary Guards' elite Quds Force, he was an architect of Iranian policy in the region.
Iran's Supreme Leader Ali Khamenei described the missile attacks as a "slap in the face" for the US and called for an end to the American presence in the Middle East.
The US strike on Soleimani also killed members of Iran-backed Iraqi militias, who have also vowed revenge.
However, US Vice-President Mike Pence told a leading media outlet that "intelligence" indicated that Iran had asked its allied militias not to attack US targets.
The US House of Representatives has scheduled a vote for Thursday on limiting President Donald Trump's ability to wage war against Iran without specific approval from Congress.
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In a letter to the UN Security Council, US Ambassador to the UN Kelly Craft said the US was ready to negotiate "with the goal of preventing further endangerment of international peace and security or escalation by the Iranian regime".
The killing of Soleimani was justified, the letter argued, under Article 51 of the UN Charter, which requires states to "immediately report" to the Security Council if any measures taken in exercising the right of self-defence.
The US would take additional action "as necessary" in the Middle East to protect its personnel and interests, the letter added.