A previously undisclosed notification to the US Congress, obtained by the Financial Times, says the ageing underwater pipelines, which link storage facilities near Basra to offshore tanker fuelling terminals, are in urgent need of back-up or repair.

“The likelihood of a worst-case catastrophic failure, subsequent collapse of Iraqi crude oil export revenue resulting in a devastating drop in the Iraqi GDP, global economic market impacts and a possible ecological and environmental disaster should warrant concern,” the document says.

The two 50km pipelines carry nearly all of Iraq's oil exports, linking the southern fields, where about three-quarters of the country's oil reserves are found, to the Gulf. Oil revenues finance more than 90 per cent of the government budget.