Unidentified gunmen have killed nine foreign nationals in southeastern Iran near the Pakistani border, the semi-official Mehr news agency reported on Saturday, amid efforts by the two countries to mend ties after tit-for-tat attacks.

Mehr said no individuals or groups had claimed responsibility for the shootings in the restless Sistan-Baluchestan province.

The Baluch rights group Haalvash said on its website that the victims were Pakistani labourers who lived at an auto repair shop where they worked. Three others were wounded, it said.

The shootings occurred as Iranian state media said the Pakistani and Iranian ambassadors had returned to their postings after being recalled when the neighbouring countries exchanged missile strikes last week aimed at what each said were militant targets.

The impoverished region has long been the scene of sporadic clashes between security forces and separatist militants and smugglers carrying opium from Afghanistan, the world's top producer of the drug.

Iran has some of the lowest fuel prices in the world and this has also led to fuel-smuggling to Pakistan and Afghanistan.