Fugitive Bosnian Serb war crimes suspect Ratko Mladic has been arrested in Serbia after 16 years on the run.
Gen Mladic, 69, was found in a village in northern Serbia where had been living under an assumed name.
He faces charges over the massacre of at least 7,500 Bosnian Muslim men and boys at Srebrenica in 1995.
Serbian President Boris Tadic said the process to extradite the former Bosnian Serb army chief to the war crimes tribunal in The Hague was under way.
Following the arrest of Radovan Karadzic in 2008, Gen Mladic became the most prominent Bosnian war crimes suspect at large.
Serbia had been under intense international pressure to arrest him.
The detention, President Tadic said, brought the country and the region closer to reconciliation, and opened the doors to European Union membership.
Mr Tadic also rejected criticism that Serbia had been reluctant to seize Gen Mladic.
"We have been co-operating with the Hague tribunal fully from the beginning of the mandate of this government," he said.
Serbian media initially reported that Gen Mladic was already on his way to the UN tribunal for the former Yugoslavia in The Hague.
But Serbian prosecutors later said the procedure to extradite him might take a week.
A spokeswoman for families of Srebrenica victims, Hajra Catic, told AFP news agency: "After 16 years of waiting, for us, the victims' families, this is a relief."
Gen Mladic is due to appear before a Serbian judge later on Thursday.
He was seized in the province of Vojvodina in the early hours of Thursday, Serbian Justice Minister Slobodan Homan told the BBC.
Serbian security sources told AFP news agency that three special units had descended on a house in the village of Lazarevo, about 80km (50 miles) north of Belgrade.
The house was owned by a relative of Gen Mladic and had been under surveillance for the past two weeks, one of the sources added.
Gen Mladic was reportedly using the assumed name Milorad Komodic.
The Belgrade broadcaster B-92 radio said he was not in disguise - unlike Mr Karadzic, who had a long beard and a ponytail when he was captured in Belgrade three years ago.
UN war crimes chief prosecutor Serge Brammertz welcomed the arrest, saying: "Today's events show that people responsible for grave violations of international humanitarian law can no longer count on impunity."
Mr Brammertz said UN prosecutors thanked the Serbian authorities for "meeting their obligations towards the tribunal and towards justice".
Gen Mladic was indicted by the UN war crimes tribunal in The Hague in 1995 for genocide over the killings that July at Srebrenica - the worst single atrocity in Europe since World War II - and other alleged crimes.
Having lived freely in the Serbian capital, Belgrade, he disappeared after the arrest of former Yugoslav President Slobodan Milosevic in 2001.
Speculation mounted that Gen Mladic would eventually be arrested when Mr Karadzic was captured in Belgrade in July 2008.
In a message from his UN cell in the Hague, Mr Karadzic said he was sorry Gen Mladic has been arrested.
The Bosnian Serb leader added that he wanted to work with him "to bring out the truth" about the Bosnian war, in a message relayed to the Associated Press by his lawyer.
In other reaction:
- US deputy national security adviser Ben Rhodes said the US was "delighted"
- UK Foreign Secretary William Hague hailed the arrest was a "historic moment"
- Nato chief Anders Fogh Rasmussen said it finally offered "a chance for justice to be done"
- French President Nicolas Sarkozy said it was "a very courageous decision by the Serbian presidency"
- Swedish Foreign Minister Carl Bildt said Serbia's EU prospects were "now brighter than ever"