WASHINGTON -- An increasingly aggressive North Korea requires an evolving defense strategy from the United States and the Republic of Korea, the heads of those two militaries said today.

In a joint press conference held at the Pentagon, US Secretary of Defense Ash Carter and South Korean Minister of National Defense Han Min-koo pledged to increase investments in maritime cooperation, cyber capabilities and tri-lateral exercises with Japan, in moves that line up with what the Pentagon is has called the third phase of the Obama administration's rebalance to the Pacific.

North Korea yesterday unsuccessfully launched what is believed to be a Musudan missile – the second unsuccessful missile launch in the last week. Speaking through a translator, Han said the repeated failures show the Musudan design still has challenges to work through.

"For political purposes, they're conducting these Musudan launches, and through these failed tests, they've shown their limits. I personally assessed that Musudan launches will continue in the future, although it has not been confirmed," Han said through a translator, adding that "We assessed that there was a high possibility that [North Korean leader] Kim Jong Un was at the site when the launch occurred."

But the threat cannot be dismissed, especially after North Korea's apparently successful nuclear test in September.

"North Korea, as you well know, is an unstable regime. And its leadership acts upon suspicious situations. Concerning North Korea's nuclear missile threats, we believe we need to change the calculus of North Korea to respond to such aforementioned threats," Han said. "As an extension of applying pressure and sanctions, through psychological operations, we intend to expose North Korea to the realities of the outside world."

Added Carter, "Any attack on America or our allies will not only be defeated, but any use of nuclear weapons will be met with an overwhelming and effective response."

In a speech last month, Carter unveiled what he called the third phase of the "rebalance to the Pacific." Key components of that plan involve building up cyber capabilities for allies in the region and increasing maritime security exercises, both of which were echoed in Thursday’s comments.

The two nations agreed to create a bilateral cyber working group task force to look for areas of bilateral cooperation, which Han indicated would begin work this month. The countries also pledged to create what Han called an "integrated research team" to seek specific maritime areas of cooperation.

Notably, Han also announced that tri-lateral cooperation between the US, Korean and Japan will expand in 2017, both on the maritime front and in terms of intelligence sharing.

"We will continue to conduct a missile warning exercise, a search-and-rescue exercise, maritime-extradition exercise that was hosted as part of this year's RIMPAC exercise in the coming year," he said.

Added Carter, "There are a number of ways in which naval cooperation can strengthen the alliance in general and the ability to respond to provocations and to conflict. So naval cooperation is very important, even as we have great cooperation already in our navies and in the air and on land, and as I mentioned, expanding into cyberspace."

Towards the end of the press event, Han was asked about recent reports that North Korea is developing a 3,000 ton submarine capable of launching ballistic missiles. While not confirming its existence, the minister said, "We're not ruling out the possibility. And we're making preparations for any potential circumstance that we may face."