Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.

Hillary Clinton called North Korea one of the world's “wicked problems” on Tuesday — and took a swipe at President Donald Trump’s tweeting habits at an appearance in New York City.

“Negotiations are critical,” Clinton said of the efforts to achieve peace with the nuclear-armed nation. “But they have to be part of a broader strategy, not just thrown off on a tweet some morning that, ‘Hey, let’s get together, you know, see if we can’t get along and maybe we can, you know, come up with some sort of idea.’ That doesn’t work.”

Related: Hillary Clinton Explains Why She Really Lost to Trump

The president said this week that he would be willing to meet with North Korean dictator Kim Jong Un and called him a "pretty smart cookie."

Trump also has used social media to ratchet up pressure on both North Korea and China as Pyongyang threatens to conduct another nuclear test.

“North Korea is looking for trouble. If China decides to help, that would be great. If not, we will solve the problem without them! U.S.A,” he tweeted last month.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

I explained to the President of China that a trade deal with the U.S. will be far better for them if they solve the North Korean problem! — Donald J. Trump (@realDonaldTrump) April 11, 2017

The former Democratic presidential candidate frequently knocked Trump for his Twitter use during the bitterly fought 2016 race. And despite having been in office more than 100 days, Trump continues to tout his surprise electoral college victory over Clinton and slam his former rival.

“If he wants to tweet about me I’m happy to be the diversion because we’ve got lots of other things to worry about. And he should worry less about the election, and my winning the popular vote, than doing some other things that would be important to the country,” Clinton said.

At the Women for Women International's gathering, Clinton told journalist Christiane Amanpour she is currently working on a book about her 2016 loss to Trump.

“It is a painful process reliving the campaign, as you might guess,” she said.

Clinton pointed to a number of factors that contributed to her stunning loss, including the role of Russia and FBI Director James Comey's letter announcing a renewed investigation into newly discovered Clinton emails just days ahead of the election that turned out to be duplicates of emails already reviewed. Misogyny also may have been a factor, Clinton acknowledged.

"I'm now back to being an activist citizen and part of the resistance,” Clinton said, referring to the anti-Trump movement.

At a Planned Parenthood gala celebrating the organization's 100-year anniversary, Clinton noted how far women's rights and access to health care have come in the past century, saying when the organization began women didn't have the right to vote.

"We live in a very different world today, and we are not going back," Clinton said.

She said the advancement of opportunities for women and girls “remains the great unfinished business of the 21st century."

"And some days it seems like it may be even more unfinished than we’d hoped," Clinton said. "Because as we speak, politicians in Washington are still doing everything they can to roll back the rights and progress we have fought so hard for over the last century."

Clinton said that "even as we are witnessing these unprecedented attacks, we are also witnessing an unprecedented outpouring of opposition and grassroots activism."

Trump late Tuesday took a swipe at Clinton on Twitter, writing: “FBI Director Comey was the best thing that ever happened to Hillary Clinton in that he gave her a free pass for many bad deeds!”

FBI Director Comey was the best thing that ever happened to Hillary Clinton in that he gave her a free pass for many bad deeds! The phony... — Donald J. Trump (@realDonaldTrump) May 3, 2017

Trump's tweet comes a night before Comey is slated to testify before the Senate Judiciary Committee on Wednesday in an oversight hearing. It is expected to touch on the investigation into any connection between Russia and Trump associates.