WELLHEADS of the richest oilfields in the north of Iraq have been mined and set with explosives ready to detonate in case of American attack, according to Western sources and Kurdish civilians fleeing the city of Kirkuk.

The operation, though denied by Iraqi officials, appears to have been under way for a fortnight and is just part of a defensive strategy intended to make Kirkuk and its environs a network of flaming canals, minefields and tank traps should US forces attack the country.

Oil was dicovered near Kirkuk in the 1920s, turning it into Iraq’s fourth-largest city. It would be a prime target for any invading army.

The majority of the wells are in fields to the east of the urban area, and two weeks ago a mysterious explosion set one wellhead alight.

The Iraqis blamed unidentified saboteurs, but a Western source in Sulaimaniyah cited an intelligence report, claiming that the explosion was the result of a faulty reserve demolition charge placed on the wellhead by the Iraqis.

“Basically, they are placing reserve demolitions on all the wellheads around Kirkuk,” he said.

“It’s standard procedure for them. You place the explosives and blow them at the last minute if you are ordered to.

“They did exactly the same in Kuwait 12 years ago. Then it took us about nine months to get the fires out.

“This time it seems that one of the charges went off prematurely.”

Smoke from the wellhead was still pouring across the sky northwards yesterday.

Earlier this week, American officials said that reserve demolitions were being placed at the wellheads, but the charge was rejected by Hussein Suleiman al-Hadithi, Iraq’s oil under-secretary. “Iraq is keen to defend its oil wealth and it is illogical that we burn our oil wealth with our own hands,” he said.

Civilians leaving Kirkuk said that a huge network of oil canals and explosive charges were being constructed as part of city defences.

Ashna Muheddin, 26, a Kurd who left the city on Monday, heading northwards to the safety of Kurdish- controlled Chamchamal 40km (25 miles) away, said: “The centre of the city already looks like a war zone. At the end of last week the Iraqis brought tankers of petrol into the streets. They are digging circular pits beside every road junction and burying the fuel tanks in them. There are soldiers everywhere, digging new minefields and bunkers inside the city. I saw mechanical diggers making long trenches and filling them with oil.”

Other Kurds fleeing Kirkuk spoke of seeing canals, up to one kilometre long, being dug at the western and eastern approaches to Kirkuk, parallel to the main roads.

Ahmed Mohammed, 24, who left the city on Sunday, said: “I saw diggers, with two guards beside each machine, laying huge pipes in trenches at Taza at the edge of Kirkuk, and Sinaea, at the western side.The trenches were huge. They were getting tankers up and filling them with oil. I saw engineers laying explosives.”

The canals would act as defensive walls of fire to block American forces moving on Kirkuk and those placed beside government and military buildings would shroud them from airstrikes. A Baath Party headquarters at Iskan, a suburb 4km east of the city centre, had two large oil pits dug beside it, according to Mr Muheddin.

He also claimed to have watched similar pits being constructed by a military base in Kirkuk’s Karama sector and at a second neighbouring Baathist office.

“They were strengthening their fortifications around each location,” he said. “Sandbagged bunkers were being made every hundred metres, manned by Baathist members with heavy machineguns and rockets.

“But I also saw two pits dug at each of those places and filled with oil. They will fire them before the bombing starts so the American jets can see nothing through the smoke.”

Meanwhile, along the Iraqi defence lines east of the city, hundreds more soldiers were being deployed as bulldozers dug tank pits for armour belonging to the Republican Guard, whose 10,000-strong Nabukhuznassir Division is based there.

Muhammad Sabir, 29, a Kurd, said: “I was buying some sheep from Arab smugglers right in front of their lines.

“The traders told me that columns of Republican Guard vehicles were moving up the other side of the hill. I could see the soldiers myself laying mines by their positions and all along the side of the main road leading to Kirkuk.

“They may run when the battle starts, but it does not look like that right now.”