As expected, U.S. Secretary of State John Kerry’s short visit to South Korea ended in the usual way, with the top American diplomat and his hosts ― namely President Park Geun-hye and Foreign Minister Yun Byung-se ― reaffirming the solid alliance against North Korea, but failing to offer measures to deal with the antagonistic regime in Pyongyang.

Despite the short one-night itinerary, Kerry’s Seoul trip drew attention because it came shortly after the North claimed that it successfully test-fired a ballistic missile from a submarine ― heightening concerns about the missile capability of the North, which had already been suspected of miniaturizing nuclear warheads.

The South Korean intelligence agency’s report that North Korean leader Kim Jong-un had executed his defense minister also raised concerns about volatility of the leadership in Pyongyang.

Kerry said that the North’s provocations, including the test of submarine-launched missile, demonstrated that the communist country was nowhere near showing the commitment to denuclearization.

“Instead, it continues to pursue nuclear weapons and ballistic missiles, it continues to break promises and make threats, and it continues to show flagrant disregard for international laws,” he said.

Regarding the report on the purge and execution of Hyon Yong-chol, he said that the world was hearing increasingly more and more “stories of grotesque, grisly, horrendous public displays of executions.”

In a joint news conference with Kerry, Yun also said they shared the view that Hyon’s execution could point to uncertainty in North Korea’s internal situation.

Then, both the U.S. and South Korea need to work out strategic measures to cope with the situation. It is regrettable in this sense that Kerry’s successive talks with Park and Yun failed to find a practicable way.

Moreover, Washington seems to prefer sticks to carrots. Kerry said that the U.S. continues to offer Pyongyang an improved bilateral relationship but it is rather “recklessly abandoning” its obligations under U.N. resolutions.

“As a result, we are indeed talking about ways to increase the pressure and increase the potential of either sanctions or other means,” Kerry said.

Given the North’s recalcitrance, frustration on this level is understandable, but we already know that sanctions did not work to stop it from pursuing its missile and nuclear ambitions.

Before coming to Seoul, Kerry said in Beijing that North Korea’s nuclear activity was one of the “most complex” global security challenges, alongside the Ebola virus and Afghanistan.

Any such complex issue must be resolved by a combination of strategic measures, not by only pressure and sanctions. Such a hard-line stance would only push the already isolated, reclusive regime further into a corner and increase tensions on the peninsula.

What comes as a relief is that while mentioning the possibility of more sanctions on the North, Kerry expressed hopes that the successful conclusion of a nuclear deal with Iran could have a positive influence on North Korea, because it would show that giving up nuclear weapons improves the domestic economy and ends isolation.

Kerry and Yun are obliged to make sure that their bosses agree on what the two governments can and should do to make North Korea a second Iran when they meet in Washington next month.