Robbie Farah, the NRL star who has called for tougher laws to fight internet trolls, has apologised for a tweet he sent last year in which he said Prime Minister Julia Gillard should be given a noose for her birthday.

It has been revealed that, in September last year, on Ms Gillard's 50th birthday, Farah responded to a tweet from former league star, now Triple M radio host, Mark Geyer, asking "what would you buy the PM for her birthday? It's her 50th today" with the words: "a noose".

Later that day he tweeted: "Some people on twitter obviously can't take a joke. Lighten up people." And the next day he tweeted "no one said anything about suicide".