Ejup Ganic is a former president of the Muslim-Croat Federation in Bosnia
Britain should apologise to a former Bosnian president for "mistreating" him in prison, the chairman of the joint presidency of Bosnia-Hercegovina said.
Former Bosnian President Ejup Ganic, 64, was arrested at Heathrow over war crimes allegations on 1 March at the request of Serbia. He was later bailed.
Haris Silajdzic, chairman of the joint presidency of Bosnia-Hercegovina, said Mr Ganic was denied basic rights.
The Foreign and Commonwealth Office declined to comment on the complaint.
But the Foreign Office said the arrest itself was a "judicial matter" and was in "no way" a political statement.
Mr Ganic is accused of killing wounded Bosnian Serb soldiers in 1992 during the Balkan wars.
His lawyers say moves to make him face trial in Serbia are politically motivated and his arrest was illegal.
Lord Justice Laws at the High Court granted Mr Ganic bail earlier on Thursday on "stringent" conditions.
Mr Silajdzic said he was "shocked" by Mr Ganic's claims he was denied access to consular assistance, to a telephone and to his medicine for three days while held in Wandsworth Prison.
Mr Ganic, a friend of Baroness Thatcher, was a wartime leader who briefly acted as president.
He was indicted last year by a Belgrade court, along with 18 others, over an incident in which 42 soldiers from the Yugoslav army were said to have been killed.
It is alleged to have happened at the start of the conflict, after Bosnia had declared independence from the Serb-led former Yugoslavia.
Serbia says the Yugoslav convoy, accompanied by UN peacekeepers, was attacked during the retreat from a Bosnian Muslim area of Sarajevo in violation of a safe passage pact.
Clare Montgomery QC, for Mr Ganic, says the allegations have already been rejected by the International Criminal Tribunal for the former Yugoslavia.
Extradition agreements give the Serbian authorities 45 days from the date of arrest to make their extradition request.
After his arrest, thousands of Bosnians protested outside the British and Serbian embassies in the Bosnian capital Sarajevo demanding his release.
Previously Westminster magistrates had refused bail on the grounds there was a danger of Mr Ganic leaving the country and he had been remanded to Wandsworth Prison.
But bailing him to appear again before Westminster magistrates on 13 April, Lord Justice Laws said that £300,000 had been provided as security by a "well-wisher" described as "a lady of substantial means".
Buckingham University vice-chancellor Dr Terence Kealey had also offered a £25,000 surety, which was accepted by the court.
Mr Ganic had attended a degree ceremony at the university, which is partnered with the Sarajevo School of Science and Technology of which he is president, hours before he was arrested.
Foreign Secretary David Miliband had underlined that the arrest was a "judicial matter" at a meeting on Thursday with Mr Silajdzic, the Foreign Office said.
The arrest "in no way amounts to a diplomatic or political statement by the British government or any UK point of view on past events in the Western Balkans", said a spokesman.
Mr Ganic's bail conditions including staying at an undisclosed London address, observing a nightly curfew and not applying for a passport or travel document.
He must also report daily to a London police station.