(Adds Mnuchin, Flake comments)
WASHINGTON, Sept 3 (Reuters) - North Koreas words and actions continue to be very hostile and dangerous to the United States, U.S. President Donald Trump said on Twitter in his first reaction after Pyongyang conducted its sixth and most powerful nuclear test on Sunday.
North Korea is a rogue nation which has become a great threat and embarrassment to China, which is trying to help but with little success, Trump said in a second tweet.
The White House said Trump's national security team was "monitoring this closely" and that the president would convene a meeting of his advisers later on Sunday.
North Korea said it had tested an advanced hydrogen bomb for a long-range missile on Sunday, setting off a manmade earthquake near the test. Japanese and South Korean officials said that tremor was about 10 times more powerful than the one picked up after the nation's last nuclear test a year ago.
There was no independent confirmation that the detonation was a hydrogen bomb rather than a less powerful atomic weapon of the kind Pyongyang has tested in the past.
Trump also rebuked South Korea on Twitter, saying "their talk of appeasement with North Korea won't work, they (North Korea) only understand one thing."
U.S. Treasury Secretary Steve Mnuchin said on Sunday that he would put together a package of new sanctions to potentially cut off all global trade with North Korea.
"If countries want to do business with the United States, they obviously will be working with our allies and others to cut off North Korea economically," Mnuchin said on Fox News.
Senator Jeff Flake, a member of the Senate Foreign Relations Committee, said on CNNs State of the Union on Sunday that the United States had no good options when it came to North Korea.
Obviously the test yesterday shows they are further along than everyone figured, said Flake, a Republican. He said sanctions did not appear to have slowed the advance of North Koreas nuclear program, but I dont think harsh rhetoric does either.
Often critical of Trump, Flake declined to address his comment about South Korea's "talk of appeasement," but said: "I think South Korea will be with us whatever we decide." (Reporting by Steve Holland and Susan Cornwell; Writing by Joel Schectman and James Oliphant; Editing by Mary Milliken and Lisa Von Ahn)