Britain has summoned the North Korean ambassador to object to the firing of a nuclear-capable missile in the direction of Japan.

A spokeswoman for the Foreign Office said the UK "fully supports the UN Security Council's strong condemnation of North Korea's recent ballistic missile launch".

The North Korean test, which saw a missile fired 500km across the Sea of Japan and was hailed as a "success" by Pyongyang, was "a threat to international security", the Foreign Office said.

"We urge North Korea to stop its provocative actions, which threaten international peace and security, and instead re-engage with the international community, and take credible, concrete steps to prioritise the well-being of its own people instead of the nuclear and ballistic missile programmes.

"The Ambassador was asked to convey this message to Pyongyang in the strongest possible terms."

Earlier on Tuesday, North Koreans celebrated the latest missile launch, which foreign experts were analysing for evidence of advancement in the country's missile capabilities.

For the next several days, North Korea will be marking the birthday of late leader Kim Jong-il, father of current leader Kim Jong-un. The holiday reaches a climax this Thursday with the "Day of the Shining Star" and will be feted with figure skating, synchronised swimming exhibitions, fireworks and mass rallies.

At the opening of a flower festival featuring a begonia named "Kimjongilia," the missile was front and centre, too.

Visitors posed and took photos in front of a painting of the missile next to a portrait of the late leader and a large arrangement of Kimjongilia flowers that were provided by a military unit. A slogan next to the missile touted the value of the North being a powerful nuclear state.

"I felt great pride and excitement when I saw the launch on TV," said Kang Kuk Hwa, who works at a greenhouse run by the North's trade ministry to grow Kimjongilia and flowers for another event held in April that features a kind of orchid named after Kim Il-sung, North Korea's "eternal president" and Kim Jong-un's grandfather.

"As long as there is a threat from the United States, we must build up our defenses," said Kang, who is 23.

The missile tested Sunday flew about 500 kilometers (310 miles) before splashing down into the Pacific and is believed to have featured several elements — including solid fuel and new mobile launching techniques — that could indicate significant advances in the country's missile capabilities. It has been widely criticized as a violation of a U.N. resolution.

Last year, the North also conducted two nuclear tests and is believed to be moving quickly closer to having a nuclear device that can be mounted on a long-range missile.

The North has repeatedly defended the nuclear and missile programs as necessary for national defense.