WASHINGTON (AP) — With North Korea, President Donald Trump puts on the charm. But with Iran, he cranks up the pressure with economic sanctions and a stronger military presence in the Persian Gulf. He has warned its leaders they are "playing with fire."

Nuclear weapons are at the heart of the difficult U.S. relations with both Pyongyang and Tehran. But it's in North Korea where Trump has more leeway and perhaps a greater chance of striking a deal.

Kim Jong Un has seemed as willing to meet with Trump as the U.S. president has been to talk and shake hands for the cameras with him. The North Korean leader jumped at the chance to meet Trump at the Demilitarized Zone between the Koreas last weekend.

Trump has made repeated overtures to Iranian leaders, too, but without the same results.

"I think Trump would be equally on a charm offensive with the Iranians if he had a dance partner," said Mark Dubowitz, an Iran nuclear deal skeptic with the Foundation for Defense of Democracies.

Also, Israel, which views Iran as its archenemy, is pressuring Trump to take a hard-line approach to Tehran, which has threatened to wipe Israel off the map. There is no big anti-North Korea lobby in the United States pressuring the White House to shun Kim's repressive government.

Trump inherited heavy U.S. sanctions on North Korea and then for months traded fiery rhetoric with Kim, saber rattling that caused jitters across the world. That has given way to flowery correspondence, meetings between the two and this weekend's historic visit when Trump became the first U.S. president to step into North Korea while in office.

Not that Pyongyang has taken big steps in return. Critics point out that North Korea has not moved to "denuclearize" as Trump has demanded. But the country has refrained from conducting nuclear tests or test-firing long-range missiles.

Trump tweeted late Monday that "our teams will be meeting to work on some solutions to very long term and persistent problems. No rush, but I am sure we will ultimately get there.

Not so smooth with Iran.

Trump campaigned on pulling the United States out of the nuclear agreement that Tehran signed with the U.S. and other world powers in 2015. He complained that the deal, which eased economic sanctions in exchange for Iran curbing its nuclear program, didn't address Iranian ballistic missile capabilities or its support of militant groups.

After failing to adjust what Trump condemned as a fatally flawed deal, the U.S. exited the agreement last year and re-imposed sanctions that had been eased when the deal was finalized under the Obama administration.

The pressure campaign evolved not like the Trump-Kim lovefest, but to what seemed like the brink of war.

With its economy diving, Iran lashed out by shooting down a $100 million, unmanned U.S. surveillance drone and attacking shipping vessels in the Persian Gulf region. Trump said he was "cocked and loaded" to retaliate with limited missile strikes but changed his mind when he learned 150 Iranians could have been killed.

He tweeted last week, "Any attack by Iran on anything American will be met with great and overwhelming force. In some areas, overwhelming will mean obliteration."

On Monday, Iran announced it now has a stockpile of more than 660 pounds (300 kilograms) of low-enriched uranium in violation of the 2015 deal. The U.S. is partly to blame because it failed to renew waivers that allowed Iran to swap its excess to other countries.

But officials say the administration is less concerned about Monday's breach than possible further violations that could reduce the time Iran would need to produce a nuclear weapon. The deal aimed to keep that "breakout time" at one year.

Iran's deputy foreign minister has warned the White House that it's naive to think Iran will wilt under pressure, or that the Iranian people will revolt and throw out its government. He said Iran will not be forced to negotiate by having a knife put to its throat.

As for North Korea, administration officials caution that Trump's charm offensive with Kim does not foreshadow a softening of its insistence that his country must not have nuclear weapons. The New York Times reported Monday that the administration might agree to a nuclear freeze as a first step toward denuclearization.

Under that scenario, which was quickly disputed by U.S. officials, North Korea would not make any new nuclear material, meaning it couldn't expand its arsenal of 20 to 60 nuclear weapons. Under such a deal, North Korea would remain a nuclear power and would still have short and long-term missiles that could threaten U.S. allies like Japan and South Korea as well as the United States.

Stephen Biegun, U.S. special envoy to North Korea, said the report was "far from accurate."

"What is accurate is not new, and what is new is not accurate. No one on our team who knows anything would speak right now anyway," he said in a statement distributed by the State Department.

Trump's hawkish national security adviser John Bolton, who has advocated a tough stance against both North Korea and Iran, also said the administration was not considering a softer approach.

However, Richard Haass, president of the Council on Foreign Relations in New York, said the fact that Bolton was in Mongolia when Trump met Kim at the DMZ suggested there is a "significant split" within the Trump administration.

Democrats have been quick to criticize Trump for his strategy with both Iran and North Korea.

"After three made-for-TV summits, we still don't have a single concrete commitment from North Korea," said former Vice President Joe Biden, who is seeking the Democratic presidential nomination. "Not one missile or nuclear weapon has been destroyed, not one inspector is on the ground. ... North Korea has continued to churn out fissile material and is no longer an isolated pariah on the world stage."

On Iran, Biden said Trump walked away from a deal that was temporarily keeping it from developing a first nuclear bomb and applied economic pressure that has led Tehran to restart its nuclear program and become more, not less aggressive.

"Trump's Iran policy has alienated us from our allies and taken us to the brink of another war in the Middle East," he said.

In its first year, the administration tried to work with Europeans allies to mend what Trump identified as flaws in the nuclear deal, such as its silence on ballistic missiles and Iran's support for destabilizing proxies around the Middle East. The effort to create a separate agreement without Iran's participation ultimately failed.

Michael McFaul, a U.S. ambassador to Russia under President Barack Obama, says that while Trump has said he's open to talks with Iran, he sees little evidence that's the case. He wonders whether complete and verifiable denuclearization is not the goal in Iran or North Korea.

"In Iran, it may be that the real objective is regime change, including the option of U.S. military action," he says.

"In North Korea, it could be that the goal is not complete denuclearization, but an outcome that allows Kim to maintain part of his nuclear arsenal while perhaps dismantling his intercontinental ballistic missile program to reduce the direct threat to U.S. national security.

"This lesser goal could help to explain why Trump is so oddly accommodating toward North Korea."

___

EDITOR'S NOTE — Riechmann and Lee report on national security for The Associated Press.

___

This story corrects the spelling of Haass.