GEOFF BENNETT: Tensions on the Korean Peninsula are running high.

This month, the U.S. and South Korea launched their largest military exercises in nearly six years.

And, in response, North Korea tested five missiles, part of a record number of tests over the last 15 months.

Nick Schifrin looks at the debate over U.S. policy in the region, as the exercises and tests continue.

NICK SCHIFRIN: Above the Korean Peninsula, a show of force.

U.S. bombers fly alongside South Korean jets to increase what the U.S. military called wartime strategic strike capabilities.

And near the North Korean border, American and South Korean troops fire together as part of 11-day-long exercises they call Freedom Shield and Warrior Shield.

LT. COL. CARMEN BUCCI, U.S. Army: A majority of the training that we have conducted today is always to ensure that we're ready to fight tonight.

NICK SCHIFRIN: But North Korea also tried to show it's ready to fight.

Last week on state TV, it tested an intercontinental ballistic missile it says can reach the entire continental U.S.

It was a family affair.

That's North Korean leader Kim Jong-un with his daughter and with his sister on the right, alongside senior officials.

In the last week, North Korea also launched what it called a simulation of a nuclear attack on South Korea after Kim reduced the threshold for preemptive strikes.

And it launched a missile from a submarine, just one of more than 115 tests in the last year, the most in North Korean history.

SUE MI TERRY, Former CIA Analyst: They have a mission to qualitatively and quantitatively advance their nuclear missile program.

They are using military exercises as a pretext, as an excuse.

When you look at the past history, they have only they have always conducted these kind of missile tests during the -- during the exercises.

NICK SCHIFRIN: Sue Mi Terry is the director of the Asia Program at the Wilson Center in Washington.

She says Kim Jong-un has no interest in diplomacy until the U.S. accepts North Korea as a nuclear weapons power.

SUE MI TERRY: They themselves said so last fall when they said, we're not coming back to talks if we are talking about denuclearization.

We will come back to the talks potentially to talk about arms control or something else, but it's not going to be about denuclearization.

NICK SCHIFRIN: But other North Korea experts believe Kim is willing to adjust his swagger if the U.S. were willing to adjust exercises and sanctions.

ROBERT GALLUCCI, Georgetown University: They're unhappy with our military exercises.

And they may, in fact, be unhappy with the failure of the United States to meet the kinds of expectations they have about starting diplomatic activity.

NICK SCHIFRIN: Ambassador Robert Gallucci is a Georgetown professor and former diplomat.

In the 1990s, he was chief U.S. negotiator of an agreement in which North Korea promised to shut down its nuclear weapons complex, in exchange for energy facilities and improved relations.

That eventually failed, as did diplomatic efforts under President Obama and President Trump's direct talks with Kim Jong-un.

Now the Biden administration has increased military exercises and regional cooperation, but also offered North Korea to meet anywhere with no preconditions.

Does that strategy make sense, do you think?

ROBERT GALLUCCI: Well, it would make sense if it was working, and it doesn't make sense since it's not.

That's better than having preconditions, but it's not as good as saying, look, we have thought about this, and we're prepared to make some moves.

And we are going to begin with the fact that we are - - have sanctions which we can manipulate.

We have military exercises which we can manipulate, and we're prepared to send you a nice positive signal here that we're prepared to make some serious changes.

NICK SCHIFRIN: Should the U.S. be willing to adjust its exercises and its sanctions in order to get North Korea to the diplomatic table?

SUE MI TERRY: I don't think so.

North Koreans are not interested in returning to the talks right now.

Kim Jong-un has made up his mind to get his technical capability to a next level before they return to talks.

NICK SCHIFRIN: North Korea's nuclear advances have increased anxiety across the border in South Korea, where President Yoon Suk-yeol and other senior officials have discussed Seoul building its own nuclear arsenal.

Oh Se-hoon is an influential member of President Yoon's party and a likely presidential candidate in 2027.

OH SE-HOON, Mayor of Seoul, South Korea (through translator): We have come to a point where it is difficult to convince people of the rationale that we should refrain from developing nuclear weapons and stick to the cause of denuclearization.

SUE MI TERRY: I think South Koreans are scared.

They can trust the Biden administration.

But, to be honest, in the future, they are concerned about what's going to happen to the United States.

Will we have another isolationist president who might talk about pulling troops out of South Korea?

NICK SCHIFRIN: For right now, the alliance is becoming more unified.

For years, South Korea and Japan had difficult relations, but, last week, their leaders resumed ties to help create a free and open Indo-Pacific.

FUMIO KISHIDA, Japanese Prime Minister (through translator): We have agreed that, under the current strategic environment, strengthening the Japan-South Korea relationship is an urgent task.

YOON SUK-YEOL, South Korean President (through translator): South Korea and Japan share the universal values of freedom, human rights, and law, and we are the closest neighbors and partners and must cooperate on security, economic issues, and global agendas.

NICK SCHIFRIN: An agenda that publicly includes countering North Korea's growing missile threat.

SUE MI TERRY: North Koreans are making all kinds of threats about preemptive use of nuclear weapons.

But if they know that United States and South Korea and Japan are closely aligned, and you cannot separate these countries, I think it would have some sort of impact.

NICK SCHIFRIN: North Korea continues to pose one of the U.S.' most difficult challenges.

And, right now, the Biden administration is not signaling any policy change, as the tests and exercises are expected to continue.

For the "PBS NewsHour," I'm Nick Schifrin.