The United States has flown two supersonic bombers over the Korean Peninsula in a show of force against North Korea following the country's latest intercontinental ballistic missile test.
The US also said it had conducted a successful test of a missile defence system located in Alaska.
The B-1 bombers were escorted by South Korean fighter jets as they performed a low-pass over an air base near the South Korean capital of Seoul before returning to Andersen Air Force Base in Guam, the US Pacific Air Forces said in a statement.
It said the mission was a response to North Korea's two missile tests this month.
Analysts said flight data from the North's second test, conducted on Friday night, showed that a broader part of the mainland United States, including Los Angeles and Chicago, is now in range of Pyongyang's weapons.
Vice president Mike Pence said on Sunday during a visit to Estonia that the US and its allies plan to increase pressure on North Korea to end its nuclear programme.
"The continued provocations by the rogue regime in North Korea are unacceptable and the United States of America is going to continue to marshal the support of nations across the region and across the world to further isolate North Korea economically and diplomatically," Mr Pence said.
"But the era of strategic patience is over. The president of the United States is leading a coalition of nations to bring pressure to bear until that time that North Korea will permanently abandon its nuclear and ballistic missile programme."
General Terrence J O'Shaughnessy, Pacific Air Forces commander, called North Korea "the most urgent threat to regional stability".
"Diplomacy remains the lead. However, we have a responsibility to our allies and our nation to showcase our unwavering commitment while planning for the worst-case scenario," Gen O'Shaughnessy said.
"If called upon, we are ready to respond with rapid, lethal and overwhelming force at a time and place of our choosing."
Senator Dianne Feinstein, a California Democrat, said that North Korea's latest test presents a clear and present danger to the United States.
"I've spent time on the intelligence and at the briefings, and done as much reading as I possibly could," said Ms Feinstein, a member of the Senate Intelligence Committee. "And I'm convinced that North Korea has never moved at the speed that this leader has to develop an ICBM."
She said the situation shows the danger of isolating a country.
"I think the only solution is a diplomatic one," she said. "I'm very disappointed in China's response, that it has not been firmer or more helpful."
The United States often sends powerful warplanes in times of heightened tensions with North Korea.
B-1 bombers have been sent to South Korea for flyovers several times this year in response to the North's banned missile tests, and also following the death of a US college student last month after he was released by North Korea in a coma.