Border guards in Saudi Arabia have been accused of killing hundreds of Ethiopian migrants trying to cross into the kingdom from Yemen, according to a report by Human Rights Watch.

The rights group cited eyewitness accounts and images of dead bodies and burial sites on migrant routes.

The United Nations has already raised concerns about Saudi forces opening fire on migrants along the country's southern border with Yemen.

Saudi Arabia has denied the allegations, calling the report "unfounded". Yemen's Houthi rebels, who allegedly smuggle migrants over the border, did not respond to requests for comment.