Seven years ago, Iran co-operated with the US in its war against the Taliban in Afghanistan. That was before being labelled by the Bush administration as part of a so-called "axis of evil." Since then, the security situation in Afghanistan has only deteriorated. Washington has signaled it will have to engage Tehran to stabilise a country that some observers say has become a battleground for the US - Iran rivalry. From Kabul, Al Jazeeras Zeina Khodr reports.