Services are taking place across Europe in the run-up to Srebrenica Memorial Day on 11 July, marking the 20th anniversary of the Srebrenica genocide.

The events that took place in July 1995 are widely considered to be the worst genocide in Europe since World War II and, in recent years, the roles of the UN and the West have been criticised.

In 1999 UN Secretary General Kofi Annan wrote: "Through error, misjudgement and an inability to recognise the scope of the evil confronting us, we failed to do our part to help save the people of Srebrenica from the Serb campaign of mass murder."

What happened at Srebrenica?

In July 1995, towards the end of the Bosnian war, thousands of Muslim Bosniaks fled to Srebrenica to escape the Bosnian Serb army. Soldiers of the Republika Srpska (VRS) were conducting a campaign of ethnic cleansing under General Ratko Mladic, intended to wipe out the non-Serb population.

See related Is Ratko Mladic guilty of war crimes and genocide in Bosnia?

Srebrenica had been declared a UN-protected "safe zone", so Bosniaks sought refuge at the camp, where 400 Dutch peacekeepers were stationed. However, when Serb troops overran the camp the outnumbered Dutch soldiers handed over hundreds of the men to the Serbs "without firing a single shot", Al Jazeera reports.

Thousands of others fled into the forest and were later rounded up by Serb forces.

The women and children were transported back to Muslim-held territories, but according to UN estimates, more than 8,000 men were executed by Bosnian Serbs, in what international courts have ruled was genocide. Many of their bodies still lie in unmarked mass graves almost two decades later.

In 2011 Ratko Mladic was arrested and is now on trial for genocide at the International Criminal Tribunal for the former Yugoslavia.

Why did no one step in?

In the aftermath of the massacre a number of different states and organisations have been criticised for their inactivity in preventing the genocide.

In June 2014 a court in The Hague ruled that Dutch soldiers were responsible for the deaths of 300 Bosniak men. But the court decided that the soldiers could only be held liable for the deaths of those men that it handed over to Mladic's troops and not those who fled into the surrounding forests.

The controversial decision prompted Munira Subasic, president of the 'Mothers of Srebrenica' group, to ask: "How is it possible to tell one mother that the Dutch state is responsible for the death of her son on one side of the wire and not for the son on the other side?"

Newly declassified documents have also exposed the policy decisions of the US, UK and France in the run-up to the massacre with The Observer reporting that the documents show that "Britain and the US decided to sacrifice Srebrenica in their efforts for peace".

The Observer also claims that the UK and the US had advance knowledge of the Serbian plans to take Srebrenica but failed to share them with the Dutch forces on the ground.

Malcolm Rifkind, then foreign secretary, has recently argued that Srebrenica was "untenable" as a safe area due to the lack of UN forces in the town. He told the Observer: "Britain increased its numbers in Bosnia and so did France, but not others. They can call them safe areas, but you have to put enough troops there to make them safe."

How is Srebrenica being remembered?

There are to be memorial services in London, Cardiff and Edinburgh organised by the charitable initiative Remembering Srebrenica, which will receive an additional donation of £1.2m from the British government to mark the occasion.

On 11 July a memorial service will be held at the Srebrenica-Potocari Memorial and Cemetery for the Victims of the 1995 Genocide in Bosnia. Dignitaries and diplomats from across the EU will attend the service.

The UK has also tabled a United Nations Security Council Resolution to mark the occasion. The resolution will be discussed on 7 July and British Ambassador to Bosnia Edward Ferguson has said the resolution "will commemorate the victims of the genocide at Srebrenica, and those who suffered on all sides in the war, and that it will encourage further steps toward reconciliation".

Reports from Russia have claimed that Serbian President Tomislav Nikolic has asked Russian President Vladimir Putin to veto the resolution due to the inappropriate wording of the text, while Sputnik News also reports that Russian Foreign Minister Sergei Lavrov has said the British draft is written in an anti-Serb tone and would cause greater friction in the Balkans.