LONDON (AFP) -- The U.N. commissioner who investigated human rights in North Korea on Friday recommended establishing a panel of experts to study how crimes against humanity in the reclusive state can be punished.

"What do you do if we bring home powerful evidence of crimes against humanity -- and a veto" from one of the five permanent members of the United Nations Security Council "prevents you taking it further? How can you deal with that problem?" said Michael Kirby at a conference in London on human rights in North Korea.

Creating a panel of experts "would be a good step because it would keep the focus on the follow up and actions on the COI (Commission of Inquiry) report" he produced, said the Australian judge.

Zeid Ra'ad al-Hussein, the U.N. high commissioner for human rights, said in December that it was essential to take cases to the International Criminal Court.

However, China, traditionally Pyongyang's closest ally, could always wield its U.N. Security Council veto.

In London, Kirby said it was vital for the international community to keep Beijing engaged because China "likes to keep talking, and there lies the hope on the issues of Korea".

The report by the COI, headed by Kirby and delivered in February 2014, concluded that human rights violations in North Korea were unparallelled in the modern world.

If there remains much to do, there have nonetheless been "a number of positive developments", said Kirby, citing notably "the establishment of a U.N. field office in Seoul to continue gathering the statements of refugees" fleeing the Pyongyang regime.

Kim Deuk-Hwan, the deputy head of mission of the South Korean embassy in London, said: "We cannot remain silent as human rights abuses continue."

He called for the full implementation of the March 2 U.N. resolution imposing new round of sanctions on North Korea after the secretive communist regime's latest nuclear and ballistic missile tests.

"The only way to change the behaviour of the intransigent regime is for the international community to speak with one voice and to act in a united fashion," he said.

"Otherwise, North Korea will never give up its nuclear and ballistic programmes. Instead they will continue to ignore the human rights of people undeterred."

The conference, hosted by the European Alliance for Human Rights in North Korea, heard from exile Kim Hyeong-soo, who fled his homeland in 2009.

The 52-year-old biophysicist worked at the Mansumugang Institute, an organisation dedicated to preserving the longevity of the Kim dynasty and the ruling elite.

He said the institute was ultra-secure, permanently guarded by armed men, protected by electric fences -- and working on some surprising areas of research.

Kim Jong-Il, who ruled the country from 1994 until his death in 2011, "liked to drink and smoke", the exile said.

He particularly liked the British brand Rothmans, "but he couldn't obtain it, so the tobacco team, they brought the tobacco plants from Africa and then developed it so that it tasted like Rothmans", he said.