The Barack Obama administration is expected to maintain its strategy of letting South Korea play a leading role in engaging North Korea through diplomacy, a former senior U.S. official said Monday.

Kurt Campbell, who served as assistant secretary of state for East Asia and Pacific affairs until February, said this stance reflects a "clear and subtle change" in Washington's approach towards Korea.

"I think in the past the leading edge of diplomacy with North Korea was often the relationship between the U.S. and North Korea," he pointed out, meeting reporters separately at the Asan Washington Forum 2013 held at the Ronald Reagan Building and International Trade Center in the U.S. capital.

The two-day event opened earlier in the day to mark the 60th anniversary of the Seoul-Washington alliance.

Campbell said, "But I think now there's a recognition that it is critically important for South Korea to play a critical role and a leading role in the diplomacy even if North Korea bucks at that suggestion that we recognize that there must be a better relationship between the North and the South."

Pyongyang has often sought to talk directly with Washington, bypassing Seoul, in what is believed to be an effort to drive a wedge between the allies.

Earlier this month, the North proposed high-level talks with the U.S., an abrupt move coming on the heels of the last-minute cancellation of inter-Korean ministerial dialogue. The Obama government rejected the North's overtures, saying it should first take steps toward denuclearization to show it's serious about pursuing dialogue.

North Korea can't expect to have a good relationship with the U.S., or other nations, "over the heads of the South Korean people, the South Korean government," said Campbell.

On Pyongyang's ongoing peace offensive, he said, it is clearly attributable to "substantial pressure from China."

"I believe there are subtle changes in Chinese approach. It's not clear that they're fundamental but there are clear signals that North Korea is exhausting Chinese patience and that Pyongyang's provocations are viewed in Beijing as contrary to the strategic interest of China," Campbell said. (Yonhap News)