Four more mass graves have been found near the southern Mexican town of Iguala, where 43 students went missing in September 2014, officials say

The discovery came during a huge operation to find the students, who disappeared after clashing with police. They were last seen being bundled into vehicles. Recently 28 burnt bodies were found in six shallow graves, but have yet not been identified. Forensic tests are expected to take weeks. Federal Attorney General Jesus Murillo Kara said that the new graves also contained burnt bodies and are in the same area as the first set of graves. He said that the security operation in Iguala, in Guerrero state, had resulted in the arrest of 34 people - mostly local police. He said that a formal search had now been launched for the town Mayor, Jose Luis Abarca Velazquez, as well as his wife and head of security. They went on leave after the clashes and have not appeared. The students were holding a protest over hiring practices when they clashed with police on September 27, 2014. A number of theories about the reasons for their disappearance have been put forward. Some think that they may have angered a local drug gang called Guerreros Unidos by refusing to pay extortion money.