SEOUL, South Korea — The intercontinental ballistic missile North Korea launched this week was a new type of missile bigger and more powerful than any the country had tested before, South Korean officials said on Thursday.

Photos from the North’s official Korean Central News Agency are providing valuable clues about the capabilities of the missile, named the Hwasong-15. North Korea said it carried a “super-large heavy warhead which is capable of striking the whole mainland of the U.S.”

North Korea’s Hwasong series represents the most successful and formidable part of its ballistic missile arsenal, and photographs of the test suggested improvements over the Hwasong-14, a missile first tested over the summer that showed the country’s capacity to strike the continental United States.

“We believe this is a new type of missile,” said Roh Jae-cheon, a spokesman for the South Korean military’s Joint Chiefs of Staff. “It looks clearly different from the Hwasong-14 in the external looks of its nose cone, the linkage between its first and second stages, and its overall size.”