It was the first time a senior US official has described the tests as a violation of UN resolutions aimed at halting North Korea's nuclear and missile programs.

"The UN resolution prohibits the launch of any ballistic missiles," Bolton said at a press roundtable. North Korea's test firings included short range ballistic missiles and so there was "no doubt" it was a violation, he added.

Bolton's comments came ahead of a four-day visit to Japan by US President Donald Trump who arrives later in the day.

Earlier this month, Kim oversaw the first flight of a previously untested weapon - a relatively small, fast missile experts believe will be easier to hide, launch and manoeuvre in flight.

Bolton said the United States was still open to talks with Kim's regime but that it had not changed its position from the one outlined at the last summit between the United States and North Korea in Hanoi.

"Trump has held the door open for Kim, the next step is for Kim to walk through it," he said.

Bolton also urged Kim to agree to a meeting with Japanese Prime Minister Shinzo Abe, which he said could help restart dialogue on North Korea's weapons programs.

An Abe Kim summit "could be substantive assistance to that", he said.

Trump, who will play golf with Abe on Sunday before watching Sumo wrestling, is expected to discuss topics ranging from North Korea to China and two-way trade when they sit down for a summit on Monday.

The two leaders will also discuss rising tensions with Iran, Bolton said.

Australian Associated Press