(CNN) Paddy Ashdown, the former leader of Britain's Liberal Democrats and former United Nations high representative for Bosnia, died Saturday evening after struggling with a short illness, according to a tweet from the Liberal Democrats' verified Twitter account. He was 77.

"This is a hugely sad day for the Liberal Democrats and for the very many people across political and public life who had immense affection and respect for Paddy," said Vince Cable, current leader of the party. "He took up unpopular causes where he was respected for his convictions, in particular promoting the rights of the citizens of Hong Kong, and -- later -- military intervention in Kosovo."

British Prime Minister Theresa May said he served his nation with great distinction.

"He dedicated his life to public service and he will be sorely missed," she said. "My thoughts and condolences are with his family and friends at this difficult time."

Ashdown served in the Royal Marines from 1959 until 1972. After he left the military he joined the UK Foreign Office for four years.

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