Turkey wants to hand Ukraine a stockpile of American cluster bombs that has been sitting in its depots since the 1980s. Moscow has asked Washington and Ankara to explain themselves.

Any such transfer would do "serious harm ... to our bilateral relations with Washington and Ankara," Russian foreign ministry spokesperson Maria Zakharova said in a statement on August 15, responding to reports that a "substantial arsenal" of US weapons and ammunition held in Turkey could go to Kyiv. Reuters reported her remarks.

The package is larger than the phrase suggests. A State Department official wrote to Congress on August 6 that "the United States Government is prepared to authorize this transfer" of 70 M39 ATACMS ballistic missiles, 2,524 M26 rockets, 47,000 M509A1 artillery projectiles and 12 M270 launchers - a roughly $256mn deal carrying more than 10mn explosive submunitions in total, according to Human Rights Watch. The munitions were produced under a 1987 US licence.

This is a way round Ukraine's ammunition problem that costs Washington nothing off its own production lines. Kyiv has spent the past year scouring the world for shells and interceptors while US and European output stays short of what the front consumes; decades-old stock held by a third country is the one large pool nobody is bidding for. It also drops any pretence that Ankara is neutral, a week after Turkey was trying to broker a moratorium on Black Sea strikes between the same two governments.

The weapons are legal for both governments to move only because neither has signed the treaty banning them. Neither the US nor Turkey is party to the 2008 Convention on Cluster Munitions, which prohibits the use, sale and export of weapons that scatter explosive submunitions across a wide area.

"Dumping obsolete cluster munitions into a conflict creates a humanitarian liability for civilians that is tragically foreseeable," said Nicole Widdersheim, deputy Washington director at Human Rights Watch, which has called on Congress to block the transfer. The group says these particular munitions are notorious for missing their targets.

That is the argument against them. Around 40% of the bomblets fail to explode on dispersal, according to Human Rights Watch, which leaves them as "de facto anti-personnel landmines" scattered across farmland long after any ceasefire - in Ukraine's case, across the same fields the country needs back in production.

Washington has form on both sides of the question. It re-enacted a moratorium on exporting cluster munitions every year from 2009 to 2023, when then-president Joe Biden set the rule aside to send the weapons to Ukraine for the first time.

Moscow's objection is not that the weapons are indiscriminate. It is that they are arriving.