A researcher at the V-Dem Institute, an independent research organization that monitors trends in democracy, has slammed President Yoon Suk Yeol's surprise declaration of martial law and warned it could strain ties with the US.

Fabio Angiolillo, a researcher at the institute, based at the University of Gothenburg in Sweden, told The Korea Herald Saturday that Yoon's declaration was “an outright attempt to curb liberal, electoral, and participatory principles of democracy.”

His remarks come amid impeachment proceedings against the president over his declaration of martial law late Tuesday, which was rescinded six hours later.

“Martial laws are exceptional measures taken during extremely dangerous times for a country. South Korea’s violent military past already saw a wide unlawful usage of martial laws as a result of coup d’etat,” said Angiolillo whose research interests center on comparative politics, political institutions, and authoritarian regimes.

“With 18 years of democratization process spanning 1982-2000, South Korean democracy is still young, and it has been repeatedly challenged already first by Park Geun-hye and now by Yoon. In short, South Korea is still fighting to find a prolonged democratic stability.”

The V-Dem Institute annually publishes the Democracy Report that describes the state of democracy in the world, with a focus on democratization and autocratization.

In a report earlier this year, the institute warned Korea was one of several countries slipping back to autocratization after several years of improvement in its democracy.

The expert also expressed concerns over cracks in the Korean-US alliance as a result of Yoon’s actions.

“The US has repeatedly said it was not aware of Yoon’s plans to declare a martial law. Yoon’s actions have likely thrown the Seoul-Washington relationship into a trust test as the two countries have been working closely together on key security issues in Asia Pacific for decades,” he said.

He suggested that Yoon, or whoever takes over power, will likely need to take steps to reassure the US amid uncertainties regarding the security situation on the Korean Peninsula, saying “The inter-Korean relations have seen a deterioration, or at least a setback, ever since Yoon took over the presidency.”

Meanwhile, the V-Dem researcher noted that Koreans have showcased remarkable democratic resilience despite the turmoil.

"Opposition leaders’ run to the parliament to vote against the martial law late at night and citizens’ spontaneous protests before the parliament against Yoon’s measures are at the very essence of South Korean democratic resilience.”

He encouraged the Assembly to endorse Yoon's impeachment.

“The opposition parties coming together with many members of the parliament that previously supported Yoon’s government and formally initiating an impeachment measure is a first, key, step to revert the dangerous authoritarian turn Yoon took,” he said, emphasizing the need for the incoming leadership that would follow to uphold democratic principles.

“I cannot foresee how the democracy indexes (for South Korea) will look like next year as our data are based on the largest survey of experts across the world, but the challenge that the opposition parties and citizens at large are now facing is how to move forward to re-gain democratic levels that South Korea lost with Yoon’s administration over the past three years.”