Foreign Affairs Minister Julie Bishop will lobby Iran to take back hundreds of failed asylum seekers held in Australian immigration detention when she makes a rare visit to Tehran next week.

Iran has so far refused to accept any forced return from Australia of thousands of Iranians who arrived by boat during the Rudd and Gillard years and have been denied refugee protection.

The government is seeking to deport failed asylum seekers in a bid to relieve the Manus Island detention centre.

Winning agreement with Iran to deport failed asylum seekers is seen as a potential breakthrough for the government to relieve the strife-prone Manus Island detention centre, where many Iranians are held.

But the Greens warn people forced to return to Iran could be in danger and have called for the government to explain any potential arrangement with Tehran.