DUBAI, Oct 7 (Reuters) - Iranian authorities have denied reports security forces killed a 16-year-old girl during protests ignited by the death of a woman in police custody, Iranian media reported on Friday, saying she committed suicide by falling off a roof.Social media reports and rights group Amnesty International have said Sarina Esmaeilzadeh was killed by security forces when she was struck with batons on the head during protests over the death of 22-year-old Mahsa Amini in morality police custody.Register now for FREE unlimited access to Reuters.comRights groups say more than 150 people have been killed, hundreds have been injured and thousands arrested in a crackdown on nationwide protests marking the biggest challenge to Iran's clerical leadership in years.The chief justice of Alborz province where Esmaeilzadeh died said a preliminary investigation showed her death was caused by suicide from a fall from the roof of a five-story building, the semi-official ISNA news agency said.Amnesty International, in a Sept. 30 report, said she was one of at least 52 people killed by security forces between Sept. 19 and Sept. 25, saying Esmaeilzadeh "died after being severely beaten in the head with batons"."