Seoul, South Korea ? South Korea’s president-elect, who has said he would be more assertive in relations with the United States, promised today to work with Washington to resolve concerns about North Korea’s nuclear weapons development.

Roh Moo-hyun was declared winner in elections Thursday that took place amid rising anti-U.S. sentiment in South Korea. During the election campaign, Roh said he was not anti-American, but insisted he would not “kowtow” to his country’s chief ally.

On the morning after his victory, Roh said the traditional friendship between South Korea and the United States must “mature and advance.”

Many experts have said Roh’s stance seeking engagement with North Korea would clash with Washington’s tougher approach with Pyongyang, which said last week that it would revive a frozen nuclear power plant previously suspected of being used to make weapons.

But today Roh promised cooperation with Washington.

“In order to resolve peacefully the problem related to North Korea’s nuclear development, we will take initiatives through close cooperation between the Republic of Korea and the United States,” he said.

Roh also indicated he would push for changes in the Status of Forces Agreement — the legal code governing the 37,000 U.S. soldiers stationed in South Korea and a key source of friction in relations. Thousands of young South Koreans participated in recent street protests related to the U.S. military presence.

“I will convey to the current Korean government and the U.S. government the sincere expectations of the Korean people and my own positions concerning the amendments to the Status of Forces Agreement,” he said.

South Korean president-Elect Roh Moo-hyun, right, and his wife, Kwon Yang-sook, celebrate his victory. Roh, a 56-year-old human rights lawyer, narrowly defeated opposition leader Lee Hoi-chang in Thursday's election.