The British Museum said Friday it had returned to Iraq a collection of 156 cuneiform tablets believed to have been looted following the US-led invasion of the country. The items mostly dated from between 2,100 BC and 1,800 BC, the London museum said in a statement, according to AFP. They were impounded by customs officials at a freight company near London Heathrow Airport in 2011. The tablets are mostly economic documents but also include letters, legal and school texts and a mathematical document. Many of them come from Irisagrig, an area that was heavily looted in the aftermath of the war. The tablets were handed over to the Iraqi ambassador Saleh Altamimi and will be sent on to the Iraq Museum. "The protection of Iraqi heritage is the responsibility of the international society which we hope to continue for future generations," Altamimi said in the statement.