A former British diplomat has accused Hillary Clinton of contributing to Iraq's disastrous meltdown during her four years as Barack Obama's foreign policy chief. 

Emma Sky, who served as an adviser to one of the top US commanders in Iraq, claims in a new book that Mrs Clinton operated a "dysfunctional" diplomatic mission to Baghdad that allowed a lapse back into sectarian warfare after elections in 2010. 

At that time Mrs Clinton was mid-way through her four-year stint as Mr Obama's Secretary of State, the equivalent position to Foreign Secretary in Britain. 

The criticisms, which come as Mrs Clinton announces her presidential bid, are contained in a book that Ms Sky, an Oxford-educated Middle East expert, is to publish next month about the seven years she spent in Iraq. 

Entitled The Unraveling: High Hopes and Missed Opportunities in Iraq, it paints an unflattering picture of the Obama administration as it tried to extricate itself from the country as hastily as possible.