The sound is deafening: a low roar as if the sky is being ripped apart by some unseen celestial force. B-52s fly without illumination, but each night in Diyarbakir, a roughshod city of more than a million Kurds in this remote corner of south-eastern Turkey, the noise is unmistakable as they thunder towards targets in Iraq.
The sound provides a backdrop to the growing tension in the area. For the past few years, Turkey's long-suffering Kurdish minority, numbering roughly ten million, has enjoyed a period of relative calm and a thawing of official attitudes towards self-determination. Now, Ankara has reverted to type. Nervous soldiers fiddle with machine-guns at military checkpoints along the main roads. The country's biggest pro-Kurdish political party, Hadep, was banned last month for alleged ties to the PKK separatist group, which Turkey views as a terrorist organisation.
In January and February alone, there were 950 political arrests here, according to Selahattin Demirtas, chairman of the Diyarbakir Human Rights Association; around 100 were tortured while in custody.
In February, seven children aged between ten and 14 were arrested and imprisoned while playing in the snow at Hakkari, a town close to the mountainous border with Iraq. Their crime was to write "No War" and "Kadek", the new acronym for the PKK, in the snow. Also in February, 14 people were killed in clashes between army and Kadek sympathisers in the towns of Lice and Idil, near Diyarbakir.
The struggle between Turks and Kurds has a long history. At the 1923 Treaty of Lausanne, which in effect created modern Turkey, the Kurds were denied minority rights granted to Jews, Christians and Armenians. Until recently the Turkish government refused even to recognise the Kurds' existence, insisting that they be known as "Mountain Turks".
During the 1980s and 1990s, guerrilla warfare took the lives of 30,000 people on both sides. Whole villages were razed in an attempt to expunge PKK sympathisers. Since the PKK leader Abdullah Ocalan was captured in 1999, an uneasy ceasefire has held sway, but about 10,000 rebels continue to operate in the mountains of northern Iraq just across the border.
Turkey fears that Iraqi Kurds may emerge from the war with their own independent state (they already have a semi-autonomous one), encouraging renewed Kurdish separatism in Turkey itself. To stop that happening, Ankara has 20,000 troops perched on its 331km border with Iraq, and insists that it has the right to send them over, ostensibly to create a buffer zone for refugees. In the last Gulf war, 500,000 Kurds fled to these mountains, a crisis for which Turkey received little help from overseas.
The Kurds fear that the Turkish army could use the Iraq war as a cover to settle old scores. The worst possibility is that a full-scale war erupts between Kurds and Turks just as the US and UK attempt to impose control on Iraq. In the winding, unlit alleys of old Diyarbakir, there is talk that Iran, fearing destabilisation of its own border area, could be dragged in.
It may be irrelevant which side fires the opening shot. Elements within both the Turkish army - which many Turks say still runs the country - and Kadek are spoiling for a fight.
People here have seen too much bloodshed to be optimistic. "In the Middle East, once gunfire has broken out it is hard to stop," says Demirtas. "And just because the US and UK began the war, it doesn't mean they will be able to stop it. There are many aggrieved groups here with different demands."
In the short term, the war is doing little for this region's stricken economy, already suffering from years of trade sanctions against neighbouring Iraq. Thousands of rusting oil-tankers and trucks are parked in muddy fields beside the approach roads to the border at Silopi, while few tourists are now prepared to venture to the resorts of western Turkey, let alone travel this far east.
At Kesistepe, a grimy village where sickly donkeys cough beside a rutted track, the grinding poverty of Turkish Kurdistan is apparent. Here at Diyarbakir's main landfill site, children as young as seven brave the overpowering stench to scavenge each morning from the freshly turned rubbish. Only the roar of another B-52 overhead interrupts them briefly from their task.