North Korea has slammed Japan's recent agreement with the United States to purchase Tomahawk cruise missiles from the country a year earlier than planned.

A commentary by the Korean Central News Agency in the ruling party's newspaper on Monday said North Korea's armed forces are "keenly watching every move of Japan."

It said, "Japan's military moves" have reached a "very grave phase."

The commentary said, "Japan has interfered in the internal affairs of other countries and stepped up the overseas advance of the Self-Defense Forces, pursuant to the US strategy of hegemony."

It also referred to security cooperation among Japan, the US and South Korea, and warned, "Japan's arrogant choice will create new challenges to its security and will result in escalating tension on the Korean Peninsula and in the region."

The commentary describes defending peace and stability in these areas as an important mission for North Korea's armed forces.

Observers say the article also appears to be aimed at justifying the country's nuclear and missile development programs.