South Korean and U.S. troops have begun five days of naval drills amid North Korea's renewal of its threat to fire missiles near the American territory of Guam.
The joint exercise come at a time of heightened tensions surrounding Pyongyang's nuclear and missile programs.
South Korea's navy says the drills that began Monday in the waters off the Korean Peninsula involve fighter jets, helicopters and 40 naval ships, including the aircraft carrier USS Ronald Reagan.
South Korean and U.S. forces regularly conduct joint exercises, though North Korea condemns them as an invasion rehearsal.
North Korea last week accused the U.S. of provoking it by mobilizing the aircraft carrier and other war assets near the peninsula.
The North said it could take military counteraction such as a salvo of missile launches into waters near Guam.
On Sunday, U.S. Secretary of State Rex Tillerson said diplomatic efforts to resolve the North Korean crisis "will continue until the first bomb drops."
That statement comes despite President Trump's tweets a couple of weeks ago that his chief envoy was "wasting his time" trying to negotiate with "Little Rocket Man," a mocking nickname Mr. Trump has given the nuclear-armed nation's leader Kim Jong Un.
"I think he does want to be clear with Kim Jong Un and that regime in North Korea that he has military preparations ready to go and he has those military options on the table. And we have spent substantial time actually perfecting those," Tillerson told CNN's "State of the Union."
"But be clear: The president has also made clear to me that he wants this solved diplomatically. He's not seeking to go to war," Tillerson said.
Recent mixed messaging from the top of the U.S. government has raised concerns about the potential for miscalculation amid the increasingly bellicose exchange of words by Trump and the North Korean leader.
But Tillerson said on the CBS News broadcast "Face the Nation" Sunday there is "absolute alignment" between the State Department and White House on policies North Korea and Iran.