* Berlin breaks post-war taboo on sending arms
* Merkel cites domestic as well an international threat
* Some political opposition, parliament to debate move
By Sabine Siebold
BERLIN, Aug 31 (Reuters) - Germany will send enough weapons to arm 4,000 Kurdish fighters in northern Iraq battling against Islamic State (IS) insurgents, whose advances threaten to destabilise the Middle East, the defence minister said on Sunday.
The equipment will include armour-piercing weapons like anti-tank rockets, thousands of assault rifles, hand grenades, mine-clearing equipment, night-vision goggles, field kitchens and tents.
"The weapons delivery is enough to supply a brigade of 4,000 soldiers," said Defence Minister Ursula von der Leyen.
Breaking with a post-war policy of not sending arms to conflict zones, Chancellor Angela Merkel says northern Iraq is an "exception" because of the nature of Islamic State's violence.
"The lives of millions of people, the stability of Iraq and the whole region and ... due to the high number of foreign fighters, our security in Germany and Europe are being threatened," read a government statement after Merkel met some of her ministers to discuss details of the aid to the Kurds.
"It is our humanitarian responsibility and in the interests of our security to help those suffering and to stop the IS."
Germany, like other European countries, is concerned about the prospect of war-hardened radicalised Muslims returning home and posing a domestic security threat.
German intelligence estimates at least 400 Germans have joined the IS. The head of the domestic intelligence agency says there is evidence that five German citizens and residents have carried out suicide attacks for the insurgents in recent months.
Germany has already shipped humanitarian aid to support Iraqi Kurds as well as defensive equipment such as helmets and body armour, but no weapons. It has sent six soldiers to the general consulate in Arbil to help coordinate the effort.
The United States is pushing for an international campaign against the IS, which has seized a third each of Iraq and Syria, declared open war against the West and has declared a caliphate in the heart of the Arab world.
Opinion polls suggest the German public has no appetite for getting involved in the conflict and Merkel has made clear she would not send combat troops there.
The delivery will take place in several tranches in safe areas not immediately affected by the war, the government said. Training on complex weapons will take place in Germany, or if that is not possible, near Arbil or in a third country.
The German opposition has warned the weapons could end up in the wrong hands and parliament will debate the aid on Monday.
The government says sending arms to the Kurds does not make it more likely Berlin would do the same for Kiev in its fight against pro-Russian rebels. Von der Leyen told a Sunday paper that they were very different conflicts.
In Ukraine "dialogue is possible", she said, while the IS "don't talk - they want to set up a caliphate and they annihilate those who think differently". (Reporting by Sabine Siebold, Stephen Brown and Annika Breidthardt; Writing by Annika Breidthardt; Editing by Stephen Brown and Robin Pomeroy)
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