The United States declined Friday to comment on the South Korean National Assembly's impeachment of President Roh Moo-hyun, calling it a "domestic and internal political matter."

State Department spokesman Richard Boucher said during a regular briefing that the matter was one that the Korean government and people need to work through.

Boucher reaffirmed, however, that Seoul-Washington relations remain "strong, stable and vital" and the two countries will continue to work together on issues of mutual concern, including the six-nation talks on North Korea's nuclear arms program.

The spokesman said U.S. Secretary of State Colin Powell and his Korean counterpart, Ban Ki-moon, spoke by telephone earlier in the day and reaffirmed to each other that the two countries would keep working together and cooperating as the political situation unfolds in Korea.

Asked what impact South Korea's presidential impeachment would have on the six-party nuclear discussions, Boucher declined to speculate, only saying that he didn't detect any change "in the current level of cooperation" between the concerned countries.