SARAJEVO, Dec 8 (Reuters) - Bosnian police arrested a wartime Muslim army commander on Tuesday on charges of failing to prevent crimes committed by foreign Islamic fighters against captive Bosnian Serb soldiers during a 1992-1995 war.

The arrest of 63-year-old retiree Sakib Mahmuljin was carried out on orders of the state war crimes prosecutor, the prosecutor's office said in a statement.

"The suspect is under investigation for acting in contravention of international humanitarian law and the Geneva Conventions while serving as a commander of the 3rd Corps of the Army of BiH," it said. Mahmuljin has denied the charges during earlier proceedings.

Many Islamic fighters, or "mujahideen", came from North Africa and the Middle East to help fellow Muslims fight against Orthodox Serbs and Catholic Croats during the Bosnian war, in which 100,000 people died.

Prosecutors said the alleged crimes dated to July-October 1995 toward the end of the war, when the 3rd Corps and a detachment of foreign fighters known as El-Mujahid carried out offensives in central Bosnia.

The El-Mujahid detachment was under the official jurisdiction of the Bosnian Army during the war, though it operated autonomously and was comprised of foreign fighters from various Islamic countries.

During the operation, members of the El-Mujahid abducted and killed 50 Bosnian Serb prisoners of war who had been previously captured by other units of the 3rd Corps, the statement read.

Mahmuljin is also charged with inhumane treatment of about 20 prisoners of war and civilians whom El-Mujahid members refused to hand over to Military Police units, the office said.

According to the office, Mahmuljin failed to prevent or punish the crimes committed by the members of the El-Mujahid Detachment despite being aware that crimes would be committed.

In 2008, the U.N. war crimes court sentenced the former chief of Bosnia's army, Rasim Delic, to three years in jail for allowing the torture of Bosnian Serb soldiers by Islamic foreign fighters.

At the time, Mahmuljin denied in local media any wrongdoing and said he did not have an effective control of the El-Mujahid detachment. The investigation against Mahmuljin was started by the Hague-based court which later transferred the lower-ranking cases to the Bosnian court. (Reporting by Maja Zuvela; Editing by Matt Robinson and Andrew Heavens)

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