Two U.S. Air Force B-1B Lancer bombers flew over the Korean Peninsula on Tuesday in a show-of-force exercise as tensions with a nuclear-armed North Korea continue to escalate.

The bombers were escorted by Japanese F-15s and South Korean F-15Ks, in what marked the first time the three types of aircraft have trained together at night, Pacific Air Forces announced.

"Flying and training at night with our allies in a safe, effective manner is an important capability shared between the U.S., Japan and the Republic of Korea and hones the tactical prowess of each nations' aviators," said Air Force Maj. Patrick Applegate, 613th Air Operation Center, according to Pacific Forces. "This is a clear demonstration of our ability to conduct seamless operations with all of our allies anytime anywhere."

In Washington on Tuesday, President Trump met with Defense Secretary Jim Mattis and Joint Chiefs Chairman Gen. Joseph Dunford to discuss a possible military respnse to North Korea's continued testing of nuclear weapons and missiles.

"The briefing and discussion focused on a range of options to respond to any form of North Korean aggression or, if necessary, to prevent North Korea from threatening the United States and its allies with nuclear weapons," the White House said in a statement Tuesday night.

The South Korean military reportedly said the bombers flew over the Korean Peninsula, but the Air Force merely said the training was near the Sea of Japan. Yonhap News Agency said the Lancers and Korean fighters flew over the East Sea and conducted air-to-ground drills before flying over the peninsula, then held a firing exercise over the Yellow Sea.

Also on Tuesday, the Navy announced that the USS Tucson, a Los Angeles-class attack submarine, pulled into U.S. Fleet Activities Chinhae, South Korea, for a port visit on Saturday.

The sub, with a crew of 150, is on a scheduled deployment in the Indo-Asia-Pacific region, the Navy said.

"The Korean-American relationship is very important and our visit to Chinhae gives us the opportunity to strengthen the outstanding relationship that exists between the U.S. and the Republic of Korea," said Cmdr. Chad Hardt, the sub's commanding officer. "My crew and I are looking forward to experiencing the exciting culture of this great Korean city."

North Korea has conducted a series of nuclear tests, the largest one occurring on Sept. 3. Pyongyang has also tested intermediate-range missiles a number of times this year.

In response, the U.S. and the international community have issued multiple new rounds of sanctions against North Korea this year.