BANJA LUKA, Bosnia (Reuters) - Thousands of Muslims flocked to the capital of Bosnia’s Serb region on Saturday for the reopening of a historic mosque destroyed during wartime, a ceremony seen as encouraging religious tolerance among deeply divided communities.

Twenty years after the devastating war between its Muslim Bosniaks, Orthodox Serbs and Catholic Croats, Bosnia remains split along ethnic lines, with rival groups blocking reconciliation and reform needed to join the European Union.

The return of Muslim believers to the rebuilt Ferhadija mosque in the largely Serb city of Banja Luka, capital of Bosnia’s autonomous Serb Republic, offered hope for change to many, although some were more cautious.

Amid tight security, about 1,000 police officers patrolled the streets as buses arrived with Muslims from across the country. Traffic was barred from the city center and alcohol banned.

Turkey’s outgoing Prime Minister Ahmet Davutoglu, whose country contributed to the cost of rebuilding, reopened the mosque in front of a congregation of up to 10,000, saying the new building sent a message of peace.

“Bosnia-Herzegovina, with its Muslims, Catholics, Orthodox and Jews, is one body, one heart. If there is any attempt to split it up, it means that this one heart would be split,” he said, apparently referring to secessionist threats by Bosnian Serbs.

The 16th-century mosque, under UNESCO protection as an outstanding example of Ottoman architecture, was blown up 23 years ago. A parking lot was built where it had stood.

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Many believe its destruction was ordered by Bosnian Serbs aiming to erase any traces of Muslim heritage in the once multi-ethnic city.

ETHNIC CLEANSING

During a ceremony to lay a foundation stone for the mosque in 2001, Serb nationalists attacked visitors and dignitaries, wounding dozens and killing one Muslim.

It took another 15 years for Bosnia’s Muslims to obtain construction permits and funds to rebuild the mosque. Thousands of pieces of rubble from the original building were used after being recovered from the Vrbas River and a garbage site where they were dumped.

The day it was leveled, May 7, is now the Day of the Mosques in Bosnia, where 614 mosques were destroyed during the 1992-95 war.

Today, only 10 percent of Banja Luka’s pre-war Muslim and Croat population remains in the city following a wartime Serb campaign of ethnic cleansing.

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Bosnian Serb President Milorad Dodik said representatives of Islamic, Orthodox, Catholic and Jewish communities “have gathered here and sent messages of peace”.

Efendi Husein Kavazovic, head of Bosnia’s Islamic community, spoke of a “triumph of light over darkness”, although he had earlier expressed doubts that reconciliation was close at hand.

Bakir Izetbegovic, the Muslim chairman of Bosnia’s three-man inter-ethnic presidency, said the rebuilt mosque was sign that Bosnia’s Muslims could return to the region.

Some residents were less sanguine, with many of Banja Luka’s Serbs apparently staying away from the ceremony.

“I only want this opening to pass peacefully and without any incident as tensions still run high,” said Tatjana Kecman, a Serb from Banja Luka.

War casts a long shadow here, with Bosnian Serb leader Radovan Karadzic jailed for genocide only in March. The United Nations says Bosnian Serb backing for secession from the fragile Bosnian state is a challenge to the 1995 peace settlement.