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.

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 forum, 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.