But scholars suspect a USA role.
North Korea reacted angrily, vowing to bolster its arsenal and mount revenge against the US.
Asean's deadlock over the statement highlights China's growing influence on the grouping at a time of uncertainty over the new U.S. administration's security priorities and whether it will try to keep China's maritime activities in check. "We warn North Korea not to test or misunderstand the will of the South Korea-U.S. alliance".
South Korea's foreign minister joined her counterparts from the United States and Japan yesterday for a meeting in Manila in which Tillerson touted efforts to persuade nations to stop using North Korean labor.
Secretary of State Rex Tillerson said last week, "We would like to sit and have a dialogue with them about the future that will give them the security they seek and the future economic prosperity for North Korea".
Ahead of Sunday's talks, Tillerson visited the Manila American Cemetery and Memorial to pay tribute to more than 17,000 U.S. and Filipino servicemen who died fighting as allies during World War II.
Critics say the most realistic solution to the North Korean issue is to resume six-party talks, in which the U.S., China, Russia, Japan and both Koreas discussed ways to denuclearize the Korean Peninsula. Pyongyang views the military exercises as rehearsals for an invasion.
And now that it's done so, Beijing is also suggesting, it's time for South Korea, too, to do its part.
North Korea is close to developing a viable nuclear deterrent against the US and other powers, which its leadership considers essential for the survival of the regime.
Would Tillerson interact with his North Korean counterpart, even informally, if they crossed paths in Manila?
The U.S. will continue to take "prudent defensive measures" to protect itself and its allies, she said.
Mr Ri was avoided by Mr Tillerson, who skipped a group dinner attended by his North Korean counterpart.
The resolution also prohibits any new joint business ventures with North Koreans, limits existing ones and blacklists 13 new North Korean individuals and entities, including its primary foreign exchange bank.More news: Beijing says USA destroyer violated China's sovereignty & security
Tillerson aide R.C. Hammond said that after a productive first day, Tillerson spent several hours preparing for Day 2. Instead, the US was represented at the dinner by Thornton, whose official title is acting assistant secretary of State for East Asia and Pacific Affairs.
Anthony Ruggiero, a former United States government adviser to six-party talks with North Korea, said the resolution failed to advance U.S. proclaimed policy and was even counterproductive.
He declined to say what Ri had told him.
Foreign Minister Wang Yi says the situation has reached "crisis point" as Pyongyang reacts aggressively to the United Nations export ban.
Ri hasn't spoken publicly since arriving in the Philippines.
On Saturday, ASEAN ministers expressed "grave concern" about escalating tensions on the Korean Peninsula, including North Korea's intercontinental ballistic missile tests in July and two recent nuclear tests.
"Now the USA mainland is on the crossroads of life and death", the commentary warned.
On Twitter, Trump writes: "The United Nations Security Council just voted 15-0 to sanction North Korea".
The centerpiece of the United Nations sanctions is a ban on North Korean exports of coal, iron, lead and seafood products - and a ban on all countries importing those products, estimated to be worth over $1 billion a year in hard currency.
The Trump administration's attempts to pressure North Korea into abandoning its nuclear and missile ambitions have so far gained little traction, and Pyongyang has only stepped up its tests, launching two ICBM tests last month.
North Korea has launched more than a dozen test missiles this year.
As US President Donald Trump demanded full and speedy implementation of the new penalties, US Secretary of State Rex Tillerson laid out a narrow path for the North to return to negotiations that could ultimately see sanctions lifted.
Mr Tillerson on Monday insisted President Kim must first stop the missile tests, but he would not set a timeframe on when this might be possible or how long North Korea might have to refrain from testing more long-range missiles.