IRAN officially denies it, but pictures tell a different tale. Aired by Al Jazeera, the Qatar-based television channel, they show ageing Iranian Phantom fighter-jets bombing in support of an Iraqi attack on Islamic State (IS) positions in Iraq. It is no secret that Iran backs both the Shia-dominated government of Iraq and the Assad regime in Syria. Yet the insertion of its aircraft into a theatre that spans both countries underlines the increasingly tangled and messy nature of the conflict, where skies are already crowded with American, Allied and Syrian jets.

Iran and America are ostensibly sworn adversaries. The Islamic Republic has even frostier relations with some of America’s Arab allies. Both sets of Iranian foes are aiding rebels fighting against the Syrian government, which is heftily supported by Iran. Yet since Iraq’s democratically elected government has welcomed both the Iranians and the American-led coalition as allies, it is not surprising that they should find themselves as de facto comrades-in-arms against the menace of IS. “We are not co-ordinating nor are we deconflicting with Iranian military,” insists a spokesman for America’s defence department, referring to the co-ordination of aircraft to avoid collisions.

In fact, American and Iranian forces have so far run little risk of fraternisation in Iraq. America has focused on intelligence, air power, training of government troops and helping to woo Sunni tribes in the west of Iraq. Iran has pumped up Shia militias that viscerally shun America, and lent small numbers of troops and advisers for operations in the east, close to its border. Interviewed by the Los Angeles Times, one prominent Iranian politician noted that Iran sees this zone—the farthest eastward advance of IS—as a buffer in which military threats “will not be tolerated.” Despite its backing for Shia militias, Iran has not stood in the way of American-backed initiatives such as the recent settling of a long and bitter dispute between officials in the Iraqi capital, Baghdad, and the Kurdish autonomous region over oil revenues.

Things are not so cosy in Syria. Coalition aircraft have not fired on Syrian government forces, which are fortified by Iranian weaponry, Iranian “advisers” and Iranian-backed Lebanese and Iraqi Shia “volunteers”. But Syria’s air force, generously restocked by Russia, mingles uncomfortably in the sky with coalition aircraft. One monitoring group reckons that coalition strikes may have killed 50 civilians in Syria since September (along with more than 700 IS fighters). Meanwhile the Syrian air force has killed at least 300 using barrel bombs alone. In the last week in November residents of Raqqa, the biggest Syrian city under IS control, endured dozens of indiscriminate daytime raids by Syrian planes, followed by precision strikes at night from the coalition. The effect is to reinforce the impression that the coalition is acting as Syria’s ally, weakening moderate forces. Instead of heeding calls from embattled mainstream rebels for the creation of a no-fly zone, Syria—and Iraq—are turning into a free-for-all zone.