An international rights group says Sudan's security forces have killed at least 60 people in more than three months of street protests calling on President Omar al-Bashir to step down.

Physicians for Human Rights says al-Bashir's forces have attacked at least seven medical facilities, arrested at least 136 health personnel, fired tear gas and other weapons into hospital wards and denied patients access to medical care.

The protests erupted in December, initially over price hikes, but later tuned into calls for al-Bashir to resign.

Security forces have responded with a fierce crackdown. The government has said that 31 have been killed but hasn't updated its tally in weeks.

The New York-based watchdog has called attacks on doctors and medical facilities an "egregious violation of human rights."