SEOUL, South Korea — The top nuclear envoys of the United States, South Korea and Japan agreed on Wednesday to ratchet up pressure on North Korea, including a more effective and creative enforcement of sanctions on the impoverished country.

The three allies also said that their efforts to curtail North Korea’s nuclear weapons ambitions would now include increasing pressure on North Korea to improve its human rights record — a highly delicate topic that they have so far kept separate from their nuclear negotiations with the North.

“We agreed on the importance of enhancing pressure and sanctions on North Korea even as we keep all diplomatic options on the table and open,” said Sung Kim, Washington’s top representative to the six-nation talks aimed at negotiating an end to the North Korean nuclear weapons program.