The United States has unveiled a photo of a nuclear-powered ballistic missile submarine(SSBN), in an apparent warning to North Korea. 

The photo posted by the U.S. Navy on social media on Friday shows the Ohio-class USS Maine receiving supplies and equipment from a helicopter in the Philippine Sea. 

The move is seen as Washington touting its nuclear deterrence capabilities and sending a strong warning against North Korea's nuclear and missile provocations. It is also in line with the opening of the Group of Seven summit in Japan.

An SSBN is one of the most secretive nuclear assets in U.S. possession and their locations are rarely disclosed.

However in the case of USS Maine, photos have been previously shared showing it enter a base in Guam on April 26, the day of the South Korea-U.S. summit, and commanders of Seoul, Washington and Tokyo on board the submarine on May 4.

The latest photo was taken on May 9, indicating the submarine, after departing from Guam in late April, has traveled to a halfway point between Guam and the Korean Peninsula.