With South Korea and the US kicking off their joint military exercise in a show of force against North Korea, Washington’s senior security and diplomacy officials have reiterated assertive stance against Pyongyang while remaining open to diplomatic solutions to calm the tension.

National Security Adviser Gen. H.R. McMaster said President Donald Trump would never allow Pyongyang to threaten the US with a nuclear weapon and that the US has been constantly refining military options against Pyongyang in the event of war. 

“The president‘s been really clear about this. He is not going to permit this rogue regime, (North Korea leader) Kim Jong-un, to threaten the United States with a nuclear weapon,” he said during his interview with Fox News on Sunday. “So he is going to do anything necessary to prevent that from happening.”

In his interview with CNN on Sunday, US Secretary of State Rex Tillerson said Trump had instructed him to pursue diplomatic efforts as well to address Pyongyang’s military threat, suggesting that such an approach would continue “until the first bomb drops.”

Those comments came amid rising concern over the possibility that North Korea might carry out another provocation in protest against the allies’ naval drill, which involves US nuclear-powered aircraft USS Ronald Reagan and its carrier strike group.

North Korea has accused the joint drill as being a dress rehearsal for invasion although the allies insisted that it was defensive in nature. On Friday, the North officials renewed its threat to launch missiles toward the US territory of Guam, saying the exercise would compel them to “take military counteraction.”

Ahn Dong-chun, another high-ranking North Korea’s official who serves as a deputy chairman of the parliament, also said on Sunday that the country’s development of nuclear weapons is necessary because of the threat posed by the United States and contends the nuclear program is for deterrence.

“Our country is being threatened, the very existence of the DPRK is at stake,” said Ahn, referring to President Trump’s speech at the UN that the US would “totally destroy” North Korea if its security is threated and forced to take action.

“Our nuclear programs are nuclear deterrence programs aimed at protecting our independence; we have no choice but to develop our nuclear programs,” Ahn said during his speech at an assembly of the Inter-Parliamentary Union in St. Petersburg, Russia, according to Russian state news agency Tass.

Pyongyang and Washington have engaged in a war of words over the past weeks, with North Korea leader Kim Jong-un calling Trump “deranged” and saying he would pay dearly for his threat in response to Trump’s UN statement.

On Monday, South Korea and the US militaries kicked off a five-day joint naval drill in the waters east and west of the peninsula. The allies’ Navies will participate in the Maritime Counter Special Operation, which is designed to defend the infiltration of North Korea’s special warfare forces.

Joining the exercise was US aircraft Ronald Reagan and two Arleigh Burke-class destroyers -- the USS Stethem and the USS Mustin. A US special warfare unit was reportedly on board in a bid to enhance their capability on a “decapitation strike” targeting Kim Jong-un and his top aides.

The carrier strike group will stage a joint exercise with South Korean warships, including Sejong the Great Aegis ship and P-3 Orion anti-submarine aircraft in the East Sea. F-15K, FA-18 and A-10 fighter jets, as well as AH-64E Apache attack helicopters, Lynx and AW-159 Wild Cat naval choppers also join the drill.

“In a response to North Korea’s enhanced exercise targeting South Korea’s northwestern island, we are going to focus on preventing North Korea’s naval infiltration and destroying them,” a military source was quoted as saying by Yonhap News Agency.

In a regular press briefing on Monday, South Korea Navy’s spokesman Cmdr. Jang Wook said the joint naval drill will be carried out in the south of the water near the Northern Limit Line, the de facto sea border between the two Koreas.

The exercise came as the US has sent a batch of its strategic assets, including nuclear submarine USS Michigan, which arrived at the southern port of Busan on Friday. Armed with Tomahawk tactical missiles, the submarine is thought to be capable of striking North Korea‘s core military facilities.

A group of stealth fighters and US bombers will also be dispatched to attend the biennial military exhibition held in Seoul. A B-1B Lancer and an F-22 Raptor will be displayed during the International Aerospace and Defense Exhibition. It will kick off on Tuesday.

By Yeo Jun-suk (jasonyeo@heraldcorp.com)