US Defence Secretary Jim Mattis says any military solution to the North Korea crisis would be "tragic on an unbelievable scale" and Washington was working internationally to find a diplomatic solution.
North Korea has defied all calls to rein in its nuclear and missile programs, even from China, its lone major ally, calling them legitimate self-defence.
The rogue state's deputy UN envoy says the US needs to roll back its "hostile policy" toward the country before there could be talks between the pair.
"As everybody knows, the Americans have gestured (toward) dialogue," North Korea's Deputy UN Ambassador Kim In Ryong told reporters on Friday. "But what is important is not words, but actions."
"The rolling back of the hostile policy towards DPRK is the prerequisite for solving all the problems in the Korean Peninsula."
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It has been working to develop a nuclear-tipped missile capable of striking the US mainland, and experts say its test on Sunday of a new missile was another important step toward that aim.
"We are going to continue to work the issue," Mattis told a Pentagon news conference.
"If this goes to a military solution, it's going to be tragic on an unbelievable scale. So our effort is to work with the UN, work with China, work with Japan, work with South Korea to try to find a way out of this situation."
The remarks were one of the clearest indicators yet that President Donald Trump's administration will seek to exhaust alternatives before turning to military action to force Pyongyang's hand.
The United States, which has 28,500 troops in South Korea to guard against the North Korean threat, has called on China to do more to rein in its neighbour.
Mattis appeared to defend China's most recent efforts, even as he acknowledged Pyongyang's march forward.
"They (North Korea) clearly aren't listening but there appears to be some impact by the Chinese working here. It's not obviously perfect when they launch a missile," Mattis said, when asked about Sunday's launch.
South Korea has said the North's missile program was progressing faster than expected, with Sunday's test considered successful in flight.
