North Korea's leader is "begging for war", the US ambassador has said at an emergency meeting of the UN Security Council.
Ambassador Nikki Haley said the US would look at countries doing business with the North and planned to circulate a resolution this week with the goal of getting it approved by September 11.
"Enough is enough. War is never something the United States wants. We don't want it now. But our country's patience is not unlimited," Ms Haley said.
"The United States will look at every country that does business with North Korea as a country, that is giving aid to their reckless and dangerous nuclear intentions."
The move came as US President Donald Trump spoke by phone with South Korean President Moon Jae-in and agreed that Sunday's underground nuclear test by North Korea was a grave provocation that was "unprecedented".
The two leaders also agreed to remove the limit on the payload of South Korean missiles.
Scheduled after North Korea said it detonated the hydrogen bomb, the emergency UN session also came six days after the council strongly condemned what it called Pyongyang's "outrageous" launch of a ballistic missile over Japan.
Less than a month ago, the council imposed its stiffest sanctions yet on the reclusive nation.
But the US resolution faces an uncertain future. Russia and China have both proposed a two-pronged approach: North Korea would suspend its nuclear and missile development, and the United States and South Korea would suspend their joint military exercises.
Washington and Seoul say the manoeuvres are defensive, but Pyongyang views them as a rehearsal for invasion.
The North recently requested a Security Council meeting about the war games.
The US says there is no comparison between its openly conducted, internationally monitored military drills and North Korea's weapons programmes, which the international community has banned.
Russian Ambassador Vassily Nebenzia told reporters after Monday's meeting that sanctions alone will not solve the issue and there need to be negotiations too.
"Resolutions aimed solely at sanctioning North Korea have not worked well before," Mr Nebenzia said.
Speaking one after the other, diplomats from France, Britain and Italy and reiterated demands for the Kim regime to halt its ballistic missile and nuclear weapons programmes and urged further sanctions.
French Ambassador Francois Delattre said France was urging the adoption of new UN sanctions, swift implementation of existing ones and new, separate sanctions by the European Union.
"Pyongyang poses a clear threat to international peace and security and is increasingly and seriously challenging the global nonproliferation regime," said Sebastiano Cardi, the UN ambassador from Italy, which heads the North Korea sanctions compliance committee.
He noted that North Korea is the only country to have tested a nuclear device in the 21st century.
The North trumpeted that its sixth nuclear test blast since 2006 was a "perfect success".
"We cannot waste any more time. And in order to do that, we need North Korea to feel the pressure, but if they go down this road there will be consequences." Japanese Ambassador Koro Bessho told reporters ahead of the council meeting.