BERLIN—Chancellor Angela Merkel on Sunday defended Germany's decision to supply weapons to forces fighting militants in northern Iraq amid concern that the arms could end up in the wrong hands.

She said Germany can't stand aside and watch a "genocide" take place, and must help those fighting the radical Sunni group that calls itself the Islamic State. German weapons would be delivered to the semiautonomous Kurdish Regional Government, she said, ruling out a direct arms delivery to the Kurdistan Workers' Party, known as PKK.

"We decided to deliver weapons in an exceptional case not seen before, where Islamic militia conduct a genocide for all to see," Ms. Merkel said during an interview with public broadcaster ARD. "When we get asked to deliver a limited amount of weapons and munitions, we can't simply say that they won't get them from us. The fighters of the Kurdish Regional Government are the ones who managed to stop the whole thing together with the Americans and others. It's no option for us to simply stand aside."

Germany said Wednesday it was prepared to export arms to Iraq to help Kurdish troops fighting against the Islamic State, and would begin delivering nonlethal equipment to Iraq in the coming days.

The move is unusual for Germany, which has adopted a pacifist stance since World War II. German law prohibits the export of weapons to conflict zones, although it permits certain exceptions, such as if Germany's foreign or security interests are at risk. Over the past days, the government has justified its decision by pointing to atrocities committed by Islamic State fighters.

Germany won't send German troops to Iraq, Ms. Merkel said. But when asked how Kurds would be trained to operate the sophisticated German weapons, Ms. Merkel wouldn't rule out that some German soldiers could conduct the training on Iraqi territory. She said no decision has been made about this yet, but the training could also take place outside Iraq.

The government has yet to convince a skeptical public about the planned arms delivery to Iraq. A recent poll published Friday showed that 67% oppose such a move while only 27% supported the government's decision.

The poll of 1,264 was conducted by Forschungsgruppe Wahlen for state broadcaster ZDF on Aug. 19 and Aug. 21, with a margin of error of plus or minus three percentage points.

—Harriet Torry in Berlin contributed to this article

WSJ