Iran has condemned the murder of a lawmaker and five others in a Lebanon car bombing, saying the blast was aimed at causing instability ahead of a crucial presidential vote.

Iran has released Kian Tajbakhsh, an Iranian-American arrested on charges of harming national security earlier this year.

Iran is testing Western intentions by working with the UN atomic watchdog to resolve a nuclear row but the opportunity for such cooperation may not be repeated, a senior Iranian official said on Thursday.