The US says 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.
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 CBS News 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.
What do the letters say?
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 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.
But Iran’s UN Ambassador Majid Takht Ravanchi said the US offer of talks was “unbelievable” while the US continued to enforce harsh economic sanctions on Iran.
Mr Trump has previously offered to hold talks with Iran without preconditions – and to meet President Hassan Rouhani. In September, Ayatollah Khamenei said Iran would never engage in bilateral talks, saying it was part of America’s policy “to put pressure on Iran”.
Ayatollah Khamenei said that if the US rejoined a landmark nuclear deal it withdrew from in 2018, it could take part in multilateral talks with Iran and the other parties to the deal.
Iran also cited Article 51 as justification for its attack on US bases.
In the Iranian letter, Mr Ravanchi wrote that Tehran “does not seek escalation or war” after exercising its right to self-defence 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,” he wrote.
