After briefing senators in a highly unusual meeting at the White House, Pentagon chief Jim Mattis, Secretary of State Rex Tillerson and Director of National Intelligence Dan Coats issued a statement that toned down military rhetoric and urged the international community to help find a solution to North Korea's nuclear program.
President Donald Trump aims to "pressure North Korea into dismantling its nuclear, ballistic missile, and proliferation programs by tightening economic sanctions and pursuing diplomatic measures with our allies and regional partners," the statement read.
"We are engaging responsible members of the international community to increase pressure on the DPRK in order to convince the regime to de-escalate and return to the path of dialogue," the statement added, using North Korea's official name.
The latest move comes as tension soars on the Korean peninsula following a series of missile launches by the North and warnings from the Trump administration that military action was an "option on the table."
Still, Pentagon officials have stressed to Trump there are no easy options for military interventions in North Korea.
WATCH: US senators react to North Korea briefing
Separately, a senior administration official told AFP that the United States is considering adding North Korea to its list of countries that are designated as "state sponsors of terrorism."
"We are looking at a broad range of options obviously across all elements of national power," the official said on condition of anonymity.
North Korea had previously been considered a state sponsor of terrorism after the bombing of a South Korean flight in 1987 but then president George W Bush removed the designation in 2008.
Australia respects allies' right to defend against North Korea: Bishop
Iran, Syria and Sudan remain on the list.
Admiral Harry Harris, who heads the Pacific Command, welcomed recent efforts by Beijing to try to defuse soaring tensions between Pyongyang and Washington, and suggested a non-military solution remained the preferred outcome.
"In confronting the reckless North Korean regime, it's critical that we're guided by a strong sense of resolve, both privately and publicly, both diplomatically and militarily," Harris said.
"All options are on the table. We want to bring Kim Jong-Un to his senses, not to his knees."
Tensions rise with competing military exercises
Meanwhile, all 100 US senators filed onto charter buses for a short ride to the White House, after being summoned to receive a classified briefing on North Korea and its nuclear weapons program. The executive mansion is an extremely rare venue for such an event.
The briefing was being led by Pentagon chief Jim Mattis, Secretary of State Rex Tillerson, Director of National Intelligence Dan Coats and General Joe Dunford, who is America's top officer and chairman of the Joint Chiefs of Staff.
"This shows how serious this is," Republican Senator Lindsey Graham said.
"We should go to the home of the commander-in-chief. This lets the Congress know this is a very big deal."
Just hours before Harris spoke, US troops in South Korea began deploying a contentious anti-missile system in South Korea that has infuriated China.
The Terminal High Altitude Area Defense (THAAD) system is being set up on a former golf course in the southern county of Seongju, and its arrival was met by hundreds of protesters, some of whom clashed with police.
Harris said the THAAD system "will be operational in the coming days, and able to better defend South Korea against the growing North Korean threat."
But China fears THAAD will weaken its own ballistic capabilities and says it upsets the regional security balance.
Chinese foreign ministry spokesman Geng Shuang told reporters THAAD "severely undermines China's strategic security interests."
"It helps in no way to achieve the denuclearization of the peninsula and regional peace and stability," he said, adding China would "take necessary measures to safeguard its own interests."
'Rain of fire'
THAAD is designed to intercept and destroy short and medium-range ballistic missiles during their final phase of flight.
Harris said the Pentagon should weigh whether to install missile interceptors on Hawaii, which could be one of the first parts of the United States in range of an improved North Korean missile.
The United States already has missile interceptors in California and Alaska that can supposedly stop any ballistic threat coming over the Pacific, but Harris said these systems need strengthening.
"In other words, we need more interceptors," Harris told the House Armed Services Committee.
Pentagon officials have stressed to Trump there are no easy options for military interventions in North Korea.
Washington has deployed an aircraft carrier strike group to the peninsula in a show of force, amid signs the North could be preparing for a sixth nuclear test.
The deployment drew widespread derision after it emerged that instead of steaming toward the peninsula, the ships actually headed in the opposite direction for a few days to train with the Australian navy.
"That's my fault on the confusion and I'll take the hit for it," Harris said.
"Where I failed was to communicate that adequately to the press and the media, so that is all on me."
Harris said the USS Carl Vinson strike group is now in the Philippine Sea just east of Okinawa, "in striking range and power projection range of North Korea if called upon to do that."
In Pyongyang's latest display of its military capabilities, leader Kim Jong-Un oversaw the country's largest-ever firing drill to mark the founding anniversary of its military, state-run media said Wednesday.
The drill saw more than 300 large-caliber self-propelled guns firing simultaneously and torpedo attacks by submarines, state-run KCNA said, demonstrating North Korea's determination to pour a "merciless rain of fire on the reckless imperialist US and its dirty followers."
Seoul held a large annual drill of its own Wednesday, involving some 100 artillery pieces, 90 armored vehicles and 50 aircraft, as well as 2,000 South Korean and US troops, the defense ministry said.
