U.S. Ambassador to the United Nations Kelly Craft wrote a letter to the U.N. Security Council on Wednesday stating the U.S. is “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.”

Craft’s letter stated that the U.S. airstrike that eliminated Iranian Islamic Revolutionary Guard Corps (IRGC) Gen. Qasem Soleimani was a legitimate act of self-defense under Article 51 of the U.N. Charter, according to Reuters.

Craft said the United States will “take additional actions in the region as necessary to continue to protect U.S. personnel and interests.”

Iran’s ambassador to the United Nations, Majid Takht Ravanchi, responded that American offers to negotiate are “unbelievable” while the U.S. continues to enforce sanctions against the regime in Tehran.

Ravanchi wrote his own letter to the U.N. describing Tuesday night’s missile attack on Iraqi bases as a “measured and proportionate military response targeting an American airbase in Iraq.” 

Ravanchi reportedly gave assurances to the Security Council that Tehran “does not seek escalation or war.” He sounded the same note in an interview with NPR published on Thursday:

Ravanchi said Iran had “acted in accordance with our rights based on the United Nations charter” in the attack early Wednesday morning local time that targeted the Ain al-Assad air base in Iraq and a second U.S. base at Irbil with some two dozen ballistic missiles.

“As far as Iran is concerned, that action was concluded last night,” he said.

Asked whether Iran was finished with its retaliatory actions, he said, “It depends on the United States.”

“If the U.S. ventures to attacking Iran again, definitely proportionate response will be taken in response to that attack,” the U.N. envoy said.

U.N. Secretary-General Antonio Guterres pledged on Wednesday to “continue his active engagement” to de-escalate tensions between the U.S. and Iran.

“It is our common duty to make every effort to avoid a war in the Gulf that the world cannot afford. We must not forget the terrible human suffering caused by war. As always, ordinary people pay the highest price,” said a statement from Guterres’ office.

“We welcome any indication that leaders are walking back from major confrontation, and are doing whatever they can, to avoid any further escalation,” U.N. spokesman Stephane Dujarric said after U.S. President Donald Trump’s Wednesday address on the situation with Iran.