Thousands of men and boys killed in the Srebrenica genocide 20 years ago will be remembered at a service at Westminster Abbey today.
More than 8,370 Bosnian Muslims were systematically murdered in the days after General Ratko Mladic and Bosnian Serb troops captured the town on July 11, 1995, during the Balkans conflict. The United Nations described it as "the worst crime on European soil since the Second World War".
Prime Minister David Cameron has led tributes and the Princess Royal will travel to Bosnia and Herzegovina on Saturday for Srebrenica Memorial Day.
Mr Cameron said: "We must never, ever forget what happened at Srebrenica. The 20th anniversary is a moment to remember the many thousands who lost their lives, to remember their families and the missing, and the fact that for so many - including the Mothers of Srebrenica - the agony continues every day, undimmed by the passage of time. We must reaffirm our determination to act to prevent genocide in the future."
At the service from midday today, organised by the UK charitable initiative Remembering Srebrenica, more than 2,000 invited guests will witness 20 candles being lit in memory of the genocide victims and hear President of the Mothers of Srebrenica association Munira Subasic will tell her story.
Lord Ashdown, who became the European Union's High Representative for Bosnia and Herzegovina in 2002, will tell the Abbey: "Nothing can diminish the culpability of those who perpetrated this genocide. But, in condemning this evil, it is also right to acknowledge our passive complicity, as members of the international community for what happened.
"Whether through error, misjudgment, an inability to comprehend, or just inattention, we stood aside when we should not have done. We should therefore remember Srebrenica, not just to bear witness to those who suffered, but also as a warning to us all of what happens when we turn our back."
The service will be followed by a Srebrenica Memorial Reception hosted by Prime Minister David Cameron at 10 Downing Street and a formal reception in the Houses of Parliament hosted by Speaker of the House John Bercow.
Foreign Secretary Philip Hammond said: "While today is a day to remember the thousands of innocent Muslims murdered 20 years ago, it reminds us that it is imperative for us to do all that we can to stop this kind of atrocity ever happening again."
About 100 events have been organised across the UK as part of Srebrenica Memorial Week and yesterday people gathered at City Hall in Belfast to mark the start. A commemorative event will be held on Wednesday in Cardiff, hosted by Wales First Minister Carwyn Jones and Scotland First Minister Nicola Sturgeon will host a memorial service at St Giles' Cathedral in Edinburgh, on Friday.
Remembering Srebrenica chairman Waqar Azmi said: "This year is the 20th anniversary of the genocide that occurred in Srebrenica - the single greatest atrocity committed on European soil since the Second World War and a brutal reminder of man's inhumanity to man.
"Today's memorial service is about honouring the victims and learning the lessons from the past to help illuminate the future by involving people of all faiths and non to help build a better, safer and cohesive society for all."