The United States' ambassador to Seoul has dismissed accusations that he tried to downplay South Korean concerns over U.S. beef imports.

Ambassador Alexander Vershbow Tuesday urged South Koreans to learn more about the scientific evidence of the safety of U.S. beef. Some South Koreans said the comment was insulting.

Vershbow said Thursday that he regrets that his "comments have been interpreted in a way that caused offense to some Koreans." He added that he has the "highest regard for the educational level of Koreans" and respects their "concerns about food safety."

Also Thursday, Korean opposition lawmakers boycotted the new parliamentary session due to the government's plans to resume imports of U.S. beef. The move effectively kept the new parliament from officially convening.

The boycott is another political burden for new conservative President Lee Myung-bak and his ruling Grand National Party. The party suffered a heavy defeat in Wednesday's local by-elections, winning just nine of the 52 seats being contested.

Mr. Lee's approval ratings have sharply declined due to public anger over the agreement to resume U.S beef imports, which were halted in 2003 after a case of made cow disease in the United States.

Last year, South Korea began importing beef from cows 30 months old or younger, but a plan to resume imports of older beef stalled this week after tens of thousands of protesters took to the streets.