BERLIN – A German judge ordered two Rwanda Hutu rebel leaders to be held in jail after they were arrested on suspicion of war crimes alleged to have occurred in the DR Congo, a prosecutor said Wednesday.

Ignace Murwanashyaka, political leader of the Democratic Forces for the Liberation of Rwanda (FDLR), and his deputy Straton Musoni, were arrested in Germany Tuesday for crimes committed between January 2008 and July this year.

"The judge tasked with deciding their detention issued a jail order and they were placed in provisional detention," the federal prosecutor's office said, without indicating where they were being held.

No time limit was imposed for their detention, it said.

The German police investigation is expected to "move in a prompt and quick" manner, said Frank Wallenta, the federal prosecutor in Karlsruhe.

The FDLR has been accused of killing civilians, rape and looting in the Democratic Republic of Congo.

The rebel group denounced the arrest of their leaders, who live in southwest Germany, as "unfair and unjustified."

"Mr Murwanashyaka and Mr Musoni are innocent of the charges against them because the FDLR are in no way involved in the atrocities committed against civilians in eastern DRC," the group said in a statement.

Some members of the FDLR fled to Democratic Republic of Congo from neighbouring Rwanda after the 1994 genocide in which 800,000 people, mostly ethnic Tutsis, were slaughtered.

Many of the group's leaders are accused of taking part in the genocide and have been actively sought by Rwanda.

Murwanashyaka's lawyer, Steffen Gallas, said "all the accusations can be refuted," adding that "extradition is impossible for judicial reasons."

German prosecutors launched an investigation into Murwanashyaka, 46, and Musoni, 48, more than a year ago since their residencies in Germany gave local authorities jurisdiction, officials said.

The arrests are not linked to an international warrant issued at the request of Rwanda, prosecutors said.

Murwanashyaka and Musoni are "strongly suspected, as members of the foreign terrorist organisation FDLR, of committing crimes against humanity and war crimes," the German prosecutors said in a statement on Tuesday.