"I am concerned, but the question is, 'How concerned?' I don’t think [war] is likely, no," Petraeus told ABC News "This Week" co-anchor Martha Raddatz in an exclusive interview Sunday on "This Week."
Petraeus said the sharper rhetoric by the U.S. toward North Korea should be seen as a "communications strategy" aimed at pushing China to help halt Kim Jong Un's nuclear weapons program.
"All of this is a communications strategy that is trying to make sure that China understands that this administration is in a very different situation than any of its predecessors," he said.
The retired general also commented on President Trump's tweeting earlier this month that Secretary of State Rex Tillerson is "wasting his time" negotiating with North Korea.
Petraeus said Tillerson’s diplomacy is focused on China's influence with the North Korean regime.
"This is aimed at China," he said. "Secretary Tillerson is undertaking the kind of strategic engagement that is necessary here to build that relationship."
Although Petraeus emphasized the importance of working with China to forestall any need for military conflict with North Korea, he said the U.S. armed services are ready if necessary to take on Kim Jong Un's forces.
"If there is some kind of military engagement, we will be the best prepared we can be. But needless to say, any possible scenario will be ugly," he said.
The former CIA director also commented on the success of U.S.-backed forces in routing ISIS from its former de facto capital of Raqqa, Syria. Such military losses will lessen the terror group's ability to recruit new fighters, Petraeus said.
"The sooner that ISIS can be shown to be a loser is the sooner that it’s no longer effective at recruiting and proselytizing and encouraging, inspiring and so forth, and that is now very much the case," Petraeus said.