US President Donald Trump and North Korean leader Kim Jong Un held a historic summit in Singapore earlier this year, signing a vaguely worded deal on denuclearisation.
But there has been little progress since, with the two countries sparring over the exact meaning of the agreement.
The isolated, impoverished North is under heavy sanctions imposed over its atomic weapons programme, which it has pursued in violation of UN resolutions.
Washington insists they must be maintained until the North denuclearises.
But US officials acknowledge enforcement of the sanctions by the North’s traditional trading partners China and Russia has eased.
Meanwhile, Seoul has said it is mulling lifting its own measures against Pyongyang.
In remarks at the opening of a meeting with Southeast Asian leaders, Pence said America’s regional “partnership also includes our pressure campaign regarding” the North.
The meeting in Singapore is also being attended by Chinese Premier Li Keqiang, Russian President Vladimir Putin and South Korean leader Moon Jae-in.
“We will very much be talking about the need to maintain the pressure programme,” a senior US official said.
“It is what got Kim Jong Un to the table. It is incredibly important that the pressure stays on.”