Bosnian police on Wednesday arrested 11 people including two regional ministers over multi-million-euro tax fraud that authorities call one of the most "complex organized criminal cases" in the nation's history.

"Eleven people were arrested while three more suspects are still being questioned," police spokeswoman Kristina Jozic told journalists.

Bosnian police arrested 16 people Wednesday on charges of joining European-based Islamists and helping them travel to fight in Syria and Iraq.

"Sixteen people were arrested" in an operation across the capital Sarajevo and several other Bosnian towns, said Kristina Jozic, a spokeswoman for the state police agency SIPA.

The presidents of Bosnia, Croatia, Serbia and Montenegro, former foes in the 1990s Balkan wars, signed on Friday a declaration pledging more support in the search for the missing from those conflicts.

The declaration, signed on the eve of the International Day of Disappeared, aims to "define the role of states in accounting for the missing from conflict and human rights abuses," it said.

Thousands gathered Sunday for a final farewell to 284 people killed in Bosnia's 1992-1995 war, after their remains were exhumed from one of the largest mass graves found in the country.

"I hope it will be easier now," said 48-year old Suad Tatarevic, who came to bury some 40 family members lost to the mass killing, including his father and six brothers.

Thousands of people gathered on Friday in Srebrenica to mark the 19th anniversary of the massacre of some 8,000 Muslim males by ethnic Serb forces, Europe's worst atrocity since World War II.

A total of 175 newly-identified massacre victims were laid to rest after a commemoration ceremony held in Potocari, just outside the ill-fated Bosnian town.

Bosnia charged 13 members of an alleged criminal gang on Friday with trafficking hundreds people to Azerbaijan, in the country's largest ever prosecution of its kind.

The group recruited more than 600 people from Bosnia, Serbia and Macedonia between 2007 and 2009, promising them work in Azerbaijan, a prosecutors' statement said.

Four former members of the Bosnian Muslim wartime forces were charged on Thursday for war crimes committed against Serb refugees at the beginning of the 1992-1995 inter-ethnic conflict.

The head of the force's sabotage unit, Muhamed Sisic, and three other members of the unit are accused of attacking a column of Serb refugees in August 1992 in the eastern region of Rogatica, Bosnia's war crime prosecutor's office said in a statement.

The death toll from cataclysmic floods in the Balkans rose by six to 57 on Friday as people returned home to salvage what belongings they could in a huge clean-up operation.

The task facing the thousands of rescue workers, volunteers and soldiers was immense, with dozens of towns and villages devastated by the region's worst natural disaster in living memory.

Floodwaters crept lower in the Balkans Thursday after the region's deadliest natural disaster in living memory, revealing widespread devastation as governments sought outside aid and warned of major damage to their economies.

As thousands of relief workers began an immense clean-up operation, the first of some 150,000 people evacuated over the past week were allowed to return to their towns and villages to pick up the pieces.

A landmine dislodged by devastating floods in the Balkans exploded in Bosnia, officials said Wednesday, hurting no one but highlighting the dangers of a huge clean-up operation as governments began counting the costs.

The device, one of an estimated 120,000 mines left over from the 1990s Yugoslav wars, went off overnight in the Brcko district of northern Bosnia, the national Mine Action Center (MAC) said.