The US has criticised a decision by Google Executive Chairman Eric Schmidt and former diplomat Bill Richardson to visit North Korea.
State Department spokeswoman Victoria Nuland said: "Frankly, we don't think the timing of this is particularly helpful," citing North Korea's launch of a long-range rocket in December.
She said Schmidt and Richardson would be travelling as private citizens, not representatives of the US Government.
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The Duke and Duchess of Cambridge met young people who have battled mental health issues on Saturday.
Former Chancellor Lord Geoffrey Howe was Margaret Thatcher's longest-serving Cabinet minister, also taking on the role of Foreign Secretary.
Lord Geoffrey Howe is known by many for his resignation speech which was seen as the catalyst which destroyed Margaret Thatcher.