VOA's national security correspondent Jeff Seldin contributed to this report.
WASHINGTON - U.S. President Donald Trump says he is "not looking for war" with Iran and willing to negotiate with its leaders without preconditions, but that under no circumstances can the Islamic Republic be allowed to mass a nuclear weapons arsenal.
Trump told NBC's Meet the Press show that if the U.S. went to war with Iran, "It'll be obliteration like you've never seen before."
"But," he added, "I'm not looking to do that."
The U.S. leader said, "Here it is. Look, you can't have nuclear weapons. And if you want to talk about it, good. Otherwise, you can live in a shattered economy for a long time."
Trump's comments, taped Friday, were aired after he announced Saturday, without providing any details, that he plans to impose "major" new sanctions on Iran on Monday. He said the sanctions would be dropped as soon as the country becomes "a productive and prosperous nation again."
Two other key U.S. officials, national security adviser John Bolton and Vice President Mike Pence, issued new warnings to Iran that Trump's last-minute decision to not militarily retaliate for Tehran's Thursday shoot-down of an unmanned U.S. drone near the Strait of Hormuz should not be viewed as a sign of "weakness."
"Neither Iran nor any other hostile actor should mistake U.S. prudence and discretion for weakness," Bolton said in Jerusalem ahead of a meeting with Israeli Prime Minister Benjamin Netanyahu.
"No one has granted them a hunting license in the Middle East," Bolton said of Iran. "Our military is rebuilt new and ready to go."
Pence told the CNN television network, "Iran must not take restraint for a lack of resolve. This is a president who hopes for the best for the Iranian people...but we will stand up to their provocations."
Bolton said existing sanctions against Tehran already are having a sharp effect on the Tehran economy.
"Sanctions are biting," he said. "Iran can never have nuclear weapons -- not against the U.S.A. and not against the world."
Embed Copy Trump Administration Signals Resolve on Iran video player.
Trump spoke with reporters Saturday at the White House before leaving for the presidential retreat at Camp David outside Washington for a meeting with top administration officials, at one point saying as soon as Tehran agreed to renounce nuclear weapons, "I'm going to be their best friend."
Trump's tone was much softer on Saturday after a week of intense actions between the U.S. and Iran.
Concern about a potential armed confrontation between the U.S. and Iran has been growing since U.S. officials recently blamed Tehran for mine attacks on two oil tankers in the Strait of Hormuz, allegations Tehran denies, and Iran's downing of the drone.
On Friday, Trump said that late Thursday he had canceled a retaliatory strike against several Iranian targets. But on Thursday, according to U.S. news accounts, Trump also approved U.S. Cyber Command attacks on an Iranian intelligence group's computer systems used to control missile and rocket launches.
After calling off the retaliatory military action, Trump tweeted that the United States was "cocked & loaded to retaliate last night on 3 different sights (sic) when I asked, how many will die. 150 people, sir, was the answer from a General. 10 minutes before the strike I stopped it," Trump tweeted, saying the action would have been disproportionate.
Pence said the U.S. was "not convinced" the downing of the drone "was authorized at the highest level" of the Iranian government. As Trump weighed how to respond last week, he said the shoot-down might have been launched on orders of a "loose and stupid" Iranian officer.
World powers have called for calm after the incidents.
German Chancellor Angela Merkel on Saturday urged for a political resolution of the crisis. "That is what we are working on," she told Reuters.
On Sunday, Britain's Middle East minister, Andrew Murrison, will travel to Tehran for talks with Iranian officials.
Britain's Foreign Office said Murrison would call for "urgent de-escalation in the region." He will also discuss Iran's threat to cease complying with the nuclear deal that the United States pulled out of last year.
James Phillips, a senior researcher at the conservative Washington-based Heritage Foundation, said he believes the immediate risk of a U.S.-Iran conflict has passed.
"It's probably over as far as the incident goes with the shoot down of the drone. But, I think if there are further provocations, the president will respond in a strong and effective manner," he said.
Phillips also said he does not expect Tehran to accept U.S. calls for negotiations while Trump continues a "maximum pressure campaign" of sanctions on Iran. "I doubt that Tehran will be serious until it sees who wins the next presidential election," he said.
The U.S. announced this week it was authorizing another 1,000 troops - including a Patriot missile battery and additional manned and unmanned reconnaissance aircraft to bolster defenses at U.S. positions in Iraq and Syria.