"The pressure campaign will continue until North Korea takes decisive steps to de-nuclearize," Tillerson said at a summit on North Korea in Vancouver. "This is a strategy that has and will require patience, but, thanks to your support, the regime is already facing costs it is having difficulty bearing."
"We cannot be complacent," said Tillerson.
The international summit on North Korea's nuclear threat is taking place with the Winter Olympics in South Korea less than a month away. The international games gave rise to talks between Pyongyang and Seoul that initially covered North Korea's participation, and then expanded to include military discussions.
Despite two false alarms about ballistic missile attacks in the last week -- one in Hawaii and one in Japan -- tensions on the peninsula have settled into a steady simmer as direct talks between the north and the south continue, but Japanese Foreign Minister Taro Kono warned against countries being lulled into thinking North Korea was changing.
Speaking at the summit, Kono warned that North Korean could be "trying to buy some time" for their nuclear and ballistic missile programs by engaging in the direct talks with South Korea, and that the international community should be clear eyed about this.
"It is not the time to ease pressure towards North Korea," he said.
He listed a number of aims Pyongyang might be pursuing by engaging with its southern neighbor, suggesting that they might be hoping to get sanctions lifted by some countries, or get financial assistance.
Pyongyang might also hope that joint military exercises staged by the US and South Korea could be canceled, Kono said. It might also hope to drive a wedge "between tough and not so tough countries," he added.
And he offered a warning. If the inter-Korean dialogue does not advance as North Korea wishes, he said, "North Korea may blame others and use it as a pretext to conduct further provocative actions."
Tillerson emphasized the US's continued objection to so-called "freeze for freeze" proposals in his remarks, which would mean the US and South Korea stop military exercises and in return, North Korea would stop missile tests. He also highlighted the need to strengthen sanctions enforcement and maritime interdiction efforts.
"We all must insist on full enforcement of UN Security Council sanctions, as this is the letter of the law," said Tillerson. "We especially urge Russia and China in this matter."
Russia and China are not present at Tuesday's summit, which was organized for UN Command sending states -- countries that assisted South Korea in the Korean War.
On whether the US would begin direct engagement with North Korea, Tillerson said, "the object of negotiations, if and when we get there, is the complete, verifiable, and irreversible de-nuclearization of North Korea. All nations here today are united around that goal."