German Chancellor Angela Merkel on Monday defended a watershed decision to send arms to Iraqi Kurds battling jihadist militants, saying Europe's own security was at stake.

Merkel told parliament that Germany's move to break with a post-war policy of refusing to send weapons into conflict zones was crucial in strife-torn Iraq, the scene of "inconceivable atrocities" against civilians.

"We have the opportunity to save lives and stop the further spread of mass murder in Iraq," Merkel said during an impassioned 25-minute speech.

"We have the chance to prevent terrorists from creating another safe haven for themselves. We must take this chance."

The German government announced late Sunday that it would send military equipment including anti-tank rocket launchers, rifles and hand grenades, to Iraqi Kurds fighting to stop Islamic State (IS) militants.

Merkel said that an estimated 400 German nationals had travelled to Iraq and Syria to fight on the side of the jihadists, who were threatening the stability of the entire region.

"We must fear these fighters could return one day" and mount attacks in European cities, she said.

"The enormous suffering of many people cries to the heavens and our own security interests are threatened."

The German leader added that if "terrorists are allowed to subjugate an area in order to create a haven for themselves and other terrorists, the danger grows for us as well".

A slippery slope?

The Sunni IS and its allies control swathes of both northern and western Iraq and neighbouring northeastern Syria, where they have waged a bloody campaign that has shocked the world.

Merkel firmly dismissed opposition accusations that the German weapons could fall into the wrong hands, or that Germany was embarking on a slippery slope toward "militarism".

"What about the acute risks posed by the terror group of IS? What is happening is more grave than what could happen," she said.

"We are faced with the choice of not taking a risk and thus accepting the spread of terror, or doing something to help those fighting vicious... terror."

After a three-hour debate in the Bundestag lower house, lawmakers overwhelmingly approved the shipment in a non-binding vote backed by Merkel's large majority.

Opposition deputies complained that the parliament had not had a real say in a vote with wide-reaching consequences for German foreign policy

The German equipment, which will be delivered in three stages, will include 30 anti-tank missile systems, 16,000 assault rifles, 8,000 pistols as well as portable anti-tank rocket launchers, the defence ministry said.

As well as weapons, Germany plans to send other items such as tents, helmets and radio equipment.

The first deliveries will be able to equip about 4,000 soldiers by the end of September.

The equipment, which has been taken out of German army reserves, is valued at 70 million euros ($92 million). A total of around 50 million euros in humanitarian assistance has also been earmarked.

Meanwhile the Bundeswehr army plans to bring a small group of Kurdish peshmerga fighters to southern Germany for a week's training with the equipment.

Merkel said Germany was also prepared to take in additional Iraqi refugees, without specifying a number.

Germany's decision follows similar moves by several other countries, including the United States, Italy, France and Britain.

However supplying military hardware is unusual for Germany which, burdened by its past aggression in two world wars, generally shies away from foreign military engagements and as a rule does not export weapons into war zones.

The government shift has been controversial among the public, with opinion polls have showing strong opposition to arms shipments to Iraq.

Sixty percent of respondents were against the idea, and only 34 percent in favour, in an Infratest dimap poll for ARD public television published Friday.