Many cried during the sombre ceremony

Government ministers, Mr Djindjic's family and friends held candles and flowers beside his grave in the Novogroblje cemetery while an Orthodox Christian priest conducted a traditional service.

Also on Sunday, Mr Djindjic's personal bodyguard, Milan Veruovic, suggested in a newspaper interview that the conspiracy to murder the prime minister had been supported by at least some Serbian security personnel.

Charges have been filed against more than 40 people over the killing of Mr Djindjic, who was shot dead by a sniper outside a government office in Belgrade on 12 March.

Police said they believed Mr Djindjic had been killed to prevent a crackdown on members of the powerful Zemun organised crime gang.

A state of emergency was declared, and more than 1,000 people were detained during raids by the Serbian police.

The authorities said the Zemun clan - with alleged links to the republic's security forces - was responsible for Mr Djindjic's murder.

Several members of Serbia's elite police unit - Red Berets or Unit for Special Operations (JSO) - were arrested.

However, the alleged mastermind of the assassination - a former special police commander Milorad Lukovic, widely known as Legija - remains at large.

The crackdown has been widely criticised by human rights groups because of the alleged torture of detainees. Last week, Amnesty International appealed to the Serbian authorities to investigate the allegations.

Bodyguard's claims

In the interview to the Sunday edition of Serbia's daily Vecernje Novosti, Mr Veruovic claimed that the government building's doors were closed and locked on the day of Mr Djindjic's assassination despite the established security procedures.

Djindjic's murder shocked the whole Serbia

Mr Veruovic - who was injured in the assassination - also said that the head of government security was nowhere to be found before Mr Djindjic's arrival.

"It had been a usual procedure that the head of government security come out of the building, open the door and greet us," Mr Veruovic told the newspaper.

"But the door was locked that day, as it should not have been," he added.