US Secretary of State Rex Tillerson will not meet his North Korean counterpart at a regional forum in Manila and will instead push to deepen Pyongyang's diplomatic isolation, a senior US official said Wednesday.

North Korea's push to build a nuclear-armed missile capable of threatening US cities has brought the region to the brink of crisis, and Washington is using every diplomatic lever to shut the program down.

But, in defiance of efforts to isolate Kim Jong-Un's pariah regime, Foreign Minister Foreign Minister Ri Yong-Ho will attend a regional security forum alongside the ASEAN ministerial meeting this weekend.

Tillerson and other key players, including China's Foreign Minister Wang Yi, will also be in the Philippine capital -- but Susan Thornton, the acting US assistant secretary of state, said the US diplomat would not take the opportunity to meet Ri.

"What we would expect to see this year at the meeting would be a general chorus of condemnation of North Korea's provocative behavior," she said.

Tillerson has no plans to meet separately with the North Koreans, she said, while at the forum itself she predicted "pretty serious diplomatic isolation directed at the North Korean foreign minister."

South East Asian diplomatic sources told AFP that Tillerson had lobbied US allies to exclude North Korea from the ASEAN regional forum, which meets to discuss Asia-Pacific security issues alongside ASEAN talks.

Thornton confirmed that Washington is seeking to further isolate Pyongyang, but admitted that there had not been time to convince its regional allies to update the guest list before the Manila talks.

"We've been going around talking to partners to talk about what more they can do to increase pressure on the regime and increase the diplomatic isolation of the regime," she told reporters.

"We've been having a serious discussion about what it would take for a member to be suspended from this organization that is dedicated to conflict prevention and preventive diplomacy.

"We'll see how that develops in the coming year. Of course it's too late for us to have that conversation, since the meeting is upon us for this year.