New U.S. Ambassador William Hagerty, a businessman close to President Donald Trump, on Thursday expressed his determination to deepen security and economic ties between his country and Japan, underlining their alliance as "ironclad."

Upon arriving at Narita airport near Tokyo, Hagerty also told a press conference that he aims to boost the bilateral partnership amid threats from North Korea. "I expect to see that partnership grow stronger in the face of the rising threats in the region," he said.

The security environment in the Asia-Pacific region has worsened amid North Korea's attempt to develop nuclear-tipped ballistic missiles that could strike as far as the mainland United States, as well as China's military buildup and territorial ambitions in the East and South China seas.

While Hagerty was tight-lipped on whether he was told by Trump on how to handle the North Korean issue, he stressed that the ability of the United States to defend itself and its allies is "beyond question."

The ambassador said that "all options are on the table," with regard to dealing with North Korea, and that international pressure on North Korea will mount even more until Pyongyang dials down its rhetoric.

He sprinkled his remarks with Japanese phrases during his 15-minute news conference, such as "Hajimemashite," which roughly translates to "Nice to meet you." His wife and four children were also there.

Ahead of his arrival, the U.S. Embassy in Tokyo released a video message from Hagerty in which he said, "There is no bilateral relationship more important to the United States than our alliance with Japan. Our commitment to the security of Japan and our economic partnership is ironclad."

On the economic front, Hagerty, who served as a key member of the Trump transition team, is expected to call for greater market access for U.S. products in Japan as part of an effort to reduce the U.S. trade deficit with the country.

Hagerty is scheduled to meet with Prime Minister Shinzo Abe on Friday, along with Marine Corps Gen. Joseph Dunford, chairman of the U.S. Joint Chiefs of Staff, in Tokyo.

Separately, Abe and Dunford are expected to discuss North Korea and affirm their countries' intent to work together in surveillance and defense in light of Pyongyang's threat last week to fire ballistic missiles across two of four main Japanese islands toward the U.S. territory of Guam in the western Pacific.

The Japanese government has welcomed Trump's appointment of Hagerty, with a senior official saying he has earned a "great deal of trust" from the president.

Hagerty built ties with Japan through a three-year posting to Tokyo from the late 1980s to early 1990s while working for the Boston Consulting Group, and in his work as commissioner of economic development for Tennessee from 2011 to 2015.

The new ambassador succeeded Caroline Kennedy, who served under President Barack Obama's administration before leaving Tokyo in January.