Serbian warlord Ratko Mladic, who is accused of ordering the genocidal massacre of 8,000 Bosnian Muslim men and boys, was arrested today after 16 years on the run.
David Cameron hailed the arrest, warning that it should serve as a lesson to the likes of Libyan dictator Muammar Gaddafi.
The Prime Minister said the capture of Mladic, who now faces trial at The Hague for crimes including the massacre at Srebrenica, was "excellent news".
The arrest came in an early-morning raid by Serbian security forces on a relative's home in a village 60 miles north-east of capital Belgrade.
Mr Cameron broke off from the G8 summit in France to tell reporters: "This is excellent news because we have to remember this man stands accused of some absolutely horrific crimes.
"People should recognise that it's right that international law has a very long reach and a very long memory, and this should send a signal to all war criminals everywhere. In the end, we will get you."
Mr Cameron added: "He is accused of the most appalling war crimes, both in terms of what happened in Srebrenica but also in Sarajevo. There is a very good reason why the long arm of international law had been looking for him for so long."
Mladic was commander of the Bosnian Serb army during the war of 1992-95 and is accused of ordering the bombardment of civilians in Sarajevo and personally leading the Srebrenica massacre.
He was indicted for war crimes including genocide in 1995 and became Europe's most wanted fugitive following the 2008 arrest of Bosnian Serb leader Radovan Karadzic, who is currently awaiting trial before the International Criminal Tribunal for the former Yugoslavia (ICTY).
Mladic was tonight in custody in Serbia awaiting extradition to The Hague, a process which is expected to take a week.
His arrest was announced by Serbian president Boris Tadic just hours before the arrival in Belgrade of European Union (EU) foreign policy chief Baroness Ashton to discuss his country's application for membership of the EU.
"Today we closed one chapter in our recent history that will bring us one step closer to full reconciliation in the region," said Mr Tadic.
The arrest was "the result of the full co-operation of Serbia with The Hague tribunal", he said.
The EU has made clear that handing Mladic over to face justice was a condition of Serbia progressing to the status of formal candidate for accession and European Commission (EC) president Jose Manuel Barroso suggested that the latest developments would smooth the way for eventual membership.
"This is great news. I was exactly one week ago in Belgrade. I had an extensive, very deep, sincere conversation with President Tadic and he promised me that he would do everything to arrest Mladic," said Mr Barroso.
"So, if this is the case, it means that he is keeping his word, so we should trust Serbia's determination also to come closer to the European Union."
Lady Ashton added: "This is an important step forward for Serbia and for international justice.
"Full co-operation with the ICTY remains essential on Serbia's path towards EU membership."
Foreign Secretary William Hague congratulated the Serbian authorities.
He said: "Ratko Mladic stands accused of terrible crimes committed in Bosnia-Herzegovina and it is right that he will now be brought to face international justice.
"We now look forward to the rapid transfer of Ratko Mladic to The Hague so that the charges against him can be heard in an international court of law. Our sympathies are with all those who lost loved ones during those conflicts.
"Today should mark the beginning of a new chapter for the countries of the western Balkans."
Colonel Bob Stewart, who commanded United Nations (UN) troops in Bosnia in 1992/93 and is now a Conservative MP, told the BBC: "It is very, very important that this man Mladic is brought to The Hague quickly, the trial starts quickly, the trial is expeditious in dealing with the matter and, actually, at the end of it justice prevails.
"I saw the result of what this man did. I saw murdered men, women and children. I saw what was happening in Srebrenica."
The international community's former High Representative for Bosnia and Herzegovina and former Liberal Democrat leader Lord (Paddy) Ashdown said: "This is a great moment for the Balkans and for international justice. Mladic was one of the two primary architects of the Balkan horrors, including the worst acts of genocide on the European mainland for the last 50 years."
For Labour, shadow foreign secretary Douglas Alexander said: "This is a welcome and important step forward for the Western Balkans and a significant moment for international justice.
"The people of the western Balkans deserve a future free from conflict and we owe it to the victims of Sarajevo and Srebrenica to ensure Mladic now faces the judgment of international law."
Chief Balkan war crimes suspects indicted by UN
General Ratko Mladic: Former Bosnian Serb military chief. Accused of orchestrating Serb atrocities throughout the Bosnian war, including the 1995 massacre at Srebrenica of some 8,000 Muslims and the deadly campaign of shelling and sniping in the capital, Sarajevo. Charged with genocide, crimes against humanity and war crimes. Arrested in Serbia today.
Radovan Karadzic: The former Bosnian Serb political leader accused together with Mladic of ultimate responsibility for Serb atrocities throughout the Bosnian war, including the Srebrenica massacre and Sarajevo bombardment. Charged with genocide, crimes against humanity and war crimes. Arrested July 21, 2008, in Serbia. Trial began October 26, 2009, and is continuing.
Slobodan Milosevic: Former Yugoslav president accused of responsibility for the Balkan wars on the 1990s. Charged with genocide, crimes against humanity, war crimes. Arrested by Serbian authorities after he was ousted from power and transferred to The Hague in 2001. Trial started February 2002. Died of a heart attack March 11, 2006, and his trial was aborted.
Biljana Plavsic: Succeeded Karadzic as Bosnian Serb president and the only woman indicted by the International Criminal Tribunal for the Former Yugoslavia. Pleaded guilty to persecution in a plea bargain. Sentenced in 2003 and released in 2009 after serving two-thirds of an 11-year sentence.
General Ante Gotovina: Senior Croatian general accused of ethnic cleansing in a 1995 military campaign to seize back land from rebel Serbs. Captured in Spain December 7, 2005, and transferred to The Hague. Convicted last month and sentenced to 24 years in prison. He has appealed his conviction.
Ramush Haradinaj: Former Kosovo prime minister. Accused of murder, rape and torture of Serbs as a commander in the Kosovo Liberation Army. Surrendered to the tribunal in March 2005. Acquitted of all charges on April 3, 2008. Appeals judges ordered a retrial, saying his trial was undermined by witness intimidation.
Goran Hadzic: Last remaining fugitive. A political leader of rebel Serbs in Croatia during the mid-1990s. Charged with murder, torture and deportation of non-Serbs from the eastern Slavonia region. Indicted in June, 2004.Reuse content