The United Nations has expressed concern about the increasingly confrontational rhetoric between the United States and Iran and called for calm.
Amid rising tensions between Washington and Tehran, U.S. President Donald Trump tweeted early on May 20, "If Iran wants to fight, that will be the official end of Iran."
Iranian Foreign Minister Mohammad Javad Zarif dismissed what he called Trump's "genocidal taunts" and warned the U.S. president not to threaten Iran.
"We are concerned about the rising rhetoric," said UN spokesman Stephane Dujarric, who cited the firing of a rocket on May 19 that struck Baghdad's Green Zone that houses foreign embassies and landed 500 meters from that of the United States as being "also a concern."
"We would ask all parties to lower the rhetoric and lower the threshold of action as well," Dujarric said.
There was no claim of responsibility for the rocket attack, which caused no casualties or significant damage.
Dujarric's remarks came amid concerns about a potential military conflict between the United States and Iran.
Washington has ordered a beefing up of U.S. military assets in the Middle East and Persian Gulf, citing " imminent threats" from Iran, and ordered the evacuation of personnel from the U.S. Embassy in neighboring Iraq
Tehran has dismissed the U.S. allegations, and accused Washington of an "unacceptable" escalation of tensions.
Both sides have said they do not want a war.
In a separate tweet on May 20, Trump said that if Tehran wants to negotiate, it will have to take the first step.
"Iran will call us if and when they are ever ready. In the meantime, their economy continues to collapse -- very sad for the Iranian people!" the U.S. president tweeted.
Iranian President Hassan Rohani was quoted by state media as saying on May 20 that he favored talks and diplomacy but not under current conditions.
"Today's situation is not suitable for talks and our choice is resistance only," Iran's IRNA news agency quoted Rohani as saying.
Later on May 20, Trump told reporters: "With Iran, we'll see what happens, but they've been very hostile. They've truly been the No.1 provocateur of terror."
"I think Iran would be making a very big mistake if they did anything. If they do something, it will be met with great force but we have no indication that they will," Trump said.
"We'll have no choice," he added.
Relations between Iran and the United States plummeted a year ago when Trump pulled out of the 2015 nuclear deal which curbed Iran's nuclear program in exchange for relief from crippling sanctions.
Since then, Washington has stepped up its rhetoric and reimposed sanctions, while the Western European parties to the accord said they remained committed to it.
In announcing the U.S. pullout from the nuclear agreement between Iran and world powers, Trump said the terms were not tough enough to prevent Iran from developing nuclear weapons and did not address Iran's missile program or Tehran's support for militants in the region.
Iran denies it supports insurgent activity, including in Yemen, and has said its nuclear program is strictly for civilian energy purposes.
Earlier this month, Iran said it was suspending several commitments under the nuclear pact, and threatened to step up uranium enrichment if European countries did not act to protect it from the effects of the U.S. sanctions.