A former US national security advisor stressed the need Thursday for South Korea to increase its defense spending to 3 percent or 3.5 percent of its gross domestic product (GDP), as Seoul and Washington are in negotiations over a defense cost-sharing deal.

Robert O'Brien, who served as national security advisor for former President Donald Trump from 2019-2021, made the remarks, as South Korea and the United States are holding their eighth round of negotiations in Seoul this week to determine Seoul's share of the cost for the stationing of US Forces Korea.

"We need our allies to pitch in. The South Koreans are up to 2.5 percent of GDP in defense," O'Brien said during a forum on China's threat to American security hosted by the Washington-based American Enterprise Institute.

"Those numbers need to go to 3 percent or 3 and a half percent, like the United States, so (that) we can burden-share with our allies," he added.

He praised Japan for increasing their defense spending "dramatically" during the administrations of Prime Minister Fumio Kishida and his predecessors, Yoshihide Suga and Shinzo Abe.

"I am sure the next (Japanese) prime minister will do the same," he said.

His remarks came amid lingering concerns that should Trump, now the Republican presidential nominee, return to the Oval Office, he could put pressure on South Korea and other allies to jack up their defense spending.

Touching on China's growing nuclear arsenal and threats from North Korea and Iran, O'Brien said that the US needs to figure out how to "increase" its nuclear capability.

"Keep in mind (that) North Korea and Iran are spinning far more centrifuges than America has. I mean, to some extent, the North Korean and Iranian nuclear programs are ahead of where we are," he said.

"Certainly, the Russians and Chinese are as well. So, we've got to get back in the nuclear game."

Regarding Chinese threats, he said that China is "racing towards nuclear parity with America."

"I think their goal is to have 1,500 strategic weapons pointed at us," he said.

O'Brien also noted the importance of US-led groupings to address various challenges from China, including the AUKUS security partnership between the US, Britain and Australia and the Quad forum involving the US, India, Japan and Australia, as well as trilateral cooperation between South Korea, the US and Japan.

"Those alliances scare the Chinese because they see us operating together," he said. "We can contain and we can push back against the Chinese when they drive wedges between us."

He also gave a positive view of the Camp David summit -- the first standalone trilateral summit between South Korea, the US and Japan in August last year.

"I give the Biden administration credit for the Camp David meeting with President Yoon (Suk Yeol) and Prime Minister Kishida and President Biden," he said.

But he claimed that the "groundwork" for that meeting was laid under the Trump administration, which he said helped keep Seoul and Tokyo together at a time of historical tensions between the two Asian allies. (Yonhap)