President Donald Trump says US military action against North Korea is not "a first choice but we'll see what happens".
His latest comments were less harsh than ones he made last month where he threatened "fire and fury" against Pyongyang.
Tensions between the two countries escalated after the regime carried out its sixth and most powerful nuclear test to date.
Over the weekend, North Korean state media claimed the country had detonated a hydrogen bomb with "perfect success".
The test drew widespread international condemnation.
UN Secretary General Antonio Guterres this week suggested: “The most dangerous crisis we face today, [is] the crisis related to the nuclear risk in relation to the Democratic People's Republic of Korea.”
Mr Trump, meanwhile, has urged China, which is North Korea's main trading partner, to put more pressure on dictator Kim Jong Un to limit his controversial missile programme.
The US leader said he has had a "strong" and "frank" conversation on the telephone with China's President Xi Jinping about North Korea.
He did not rule out military strikes, but indicated other options for pressure would come first.
Mr Trump 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."
He added: "I believe that President Xi agrees with me 100%. We had a very, very frank and very strong phone call."
