The Oscar-winning documentary film-maker Laura Poitras is suing the US government demanding to know why she has repeatedly been subjected to "Kafkaesque harassment" at airports across the world.

Poitras, 51, said she had been held at borders more than 50 times between 2006 and 2012, often for hours at a time. At various times she alleges being told by officials that she was on a "no fly" list, having her electronic equipment confiscated and not returned for 41 days, and being threatened with handcuffs for taking notes. The latter incident took place when she was working on a film about the WikiLeaks founder Julian Assange.

Poitras said she was launching the legal action, which demands the release of all documentation held on her tracking, targeting and questioning by agencies over the six year period, following the failure of a 2013 freedom of information request.