Amid the nuclear and missile threat posed by North Korea, Defense Minister Itsunori Onodera said Monday that Japan is facing its toughest security environment since World War II, and pledged to resolutely protect its territory.

"It's important to work together with other nations to maintain pressure and sanctions, to achieve North Korea's complete, verifiable and irreversible denuclearization and its abandonment of weapons of mass destruction and every ballistic missile," Onodera said during an inspection of the Maritime Self-Defense Force's base in Yokosuka, Kanagawa Prefecture.

"Together with strong ties to the United States, the Defense Ministry and the SDF are beefing up our country's defense capacity, while making our best efforts to deal with the security environment concerning North Korea," he said.

Onodera, who oversees the Self-Defense Forces, inspected the submarine rescue ship Chiyoda, commissioned in March, and sent off young graduates from JMSDF Officer Candidate School on an ocean navigation training course that will take them to at least 10 countries over 163 days.

Onodera, who began his second term as defense chief last August, added that the security environment "has become even tougher" than his first stint from 2012 to 2014, saying China and Russia have been increasingly threatening to Japan in recent years.

"China is strengthening and spreading its military force over a wider area, and is expanding and increasing its maritime and airspace activities," Onodera said, explaining that a submarine and a vessel, both from China, entered the contiguous zone near the Japan-administered Senkaku Islands in January, and that fighter jets from the aircraft carrier Liaoning were spotted for the first time in the Pacific Ocean last month.

"Meanwhile, Russia in recent years has been modernizing its weapons — including its nuclear arms — not just in Europe but also close to our country," he said.