Donald Trump has warned the United States will no longer tolerate North Korea's actions but says the use of military force against Pyongyang isn't his "first choice".
His comment appears in line with classified briefings to Congress in which Trump's top national security aides - Defense Secretary Jim Mattis, Secretary of State Rex Tillerson and Dan Coats, the director of national intelligence - stressed the search for a diplomatic solution to the crisis, lawmakers said.
The White House has also set aside, for now, consideration of exiting a free trade pact with South Korea, a senior White House official says.
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In a flurry of phone calls with world leaders days after North Korea's sixth and most powerful nuclear test, Trump and Chinese President Xi Jinping committed to "take further action with the goal of achieving the denuclearisation of the Korean peninsula," the White House said.
"President Xi would like to do something. We'll see whether or not he can do it. But we will not be putting up with what's happening in North Korea," Trump told reporters on Wednesday.
"I believe that President Xi agrees with me 100 per cent."
Asked whether he was considering a military response to North Korea, Trump said: "Certainly, that's not our first choice, but we will see what happens."
Xi, who has been under pressure from Trump to do more to curb North Korea's nuclear and missile programs, told Trump during their 45-minute call that the North Korean issue must be resolved through "dialogue and consultation."
The focus on negotiations by China, North Korea's main trading partner, contrasted with Trump's assertions over the last few days that now was not the time for talks with North Korea while pressing instead for increased international pressure on Pyongyang.
The US and South Korea have asked the UN to consider tough new sanctions on North Korea after Sunday's nuclear test, which Pyongyang said was an advanced hydrogen bomb.
Russian President Vladimir Putin insisted on Wednesday that resolving the North Korean nuclear crisis was impossible with just sanctions and pressure.
Putin met South Korea's Moon Jae-in on the sidelines of an economic summit in the Russian city of Vladivostok, as international concern mounts about the chance of further missile tests before a weekend anniversary in the north.
Putin echoed other world leaders in denouncing North Korea's latest nuclear bomb test.
"Pyongyang's missile and nuclear program is a crude violation of UN Security Council resolutions, undermines the non-proliferation regime and creates a threat to the security of northeastern Asia," Putin said at a news conference.
"At the same time, it is clear that it is impossible to resolve the problem of the Korean peninsula only by sanctions and pressure," he said.
No headway could be made without political and diplomatic tools, Putin said.
Moon, who took office this year advocating a policy of pursuing engagement with North Korea, has come under increasing pressure to take a harder line and has asked the UN to consider tough new sanctions after the latest test.
The US wants the Security Council to impose an oil embargo on North Korea, ban textile exports and the hiring of North Korean labourers overseas, and freeze the assets of leader Kim Jong Un, according to a draft resolution seen by Reuters on Wednesday.
