By Agence France-Presse
Joseph Yun's comments came after US Secretary of State Rex Tillerson created a stir by appearing to open a door to direct talks with the North without preconditions -- a major policy shift that the White House swiftly rowed back on.
"It's very hard to discern what their intent is without, as I said, having a real dialogue," Yun, the US Special Representative on North Korea policy, said of the reclusive regime.
"We are open to dialogue. And we hope they will agree to have a dialogue," he told reporters in Bangkok.
It is necessary to exercise both "direct diplomacy as well as sanctions" to rein in the pariah state's nuclear programme, he added.
Yun is in Bangkok as part of a December 11-15 trip that also included a stop in Japan, as Washington seeks to shore up regional support for its "maximum pressure" campaign in response to Pyongyang's increasingly powerful nuclear and ballistic missile tests.
Tillerson has driven the global diplomatic effort to stifle the North's economy through a series of UN sanctions.
But the top diplomat appeared to soften his stance earlier this week, saying Washington was ready to negotiate with the North without preconditions, following a "period of calm".
When asked whether Pyongyang would need to meet any specific or even minimum prerequisites before a dialogue could begin, Yun said:
"My boss's statement... addresses that. I think we have to start, and he mentioned we are open to dialogue, and let's see how they respond."
China -- the North's sole ally and economic lifeline -- and Russia responded positively to Tillerson's remarks, even after the White House appeared to undermine his proposal by saying US President Donald Trump's "views on North Korea have not changed".
During his first year in office Trump has repeatedly lobbed threats at North Korean leader Kim Jong-Un, using fiery rhetoric that clashes with Tillerson's diplomatic approach.
In October the American president dismissed his Secretary of State's push for talks with the North.
He tweeted that Tillerson was "wasting his time trying to negotiate with Little Rocket Man" -- his favoured epithet for Kim.