President Muhammudu Buhari, who recently assumed office, continued his efforts to reduce Nigerian corruption this month. He announced on 10 July that himself and Vice-President Yemi Osinbajo will take a 50 per cent salary reduction compared to their predecessor's wages. President Buhari also appointed new military chiefs, in hope of transferring leadership to figures who will be able to tackle Boko Haram more effectively than the previous heads of the army, navy, and air force. The Nigerian National Petroleum Corporation (NNPC) has taken action to stifle illegal crude oil trading by banning 113 oil tankers from its country's waters. Nigeria marked a year without recording new cases of polio this July, making them eligible for removal from the World Health Organization (WHO)'s list of countries where the disease is endemic. Reports of Boko Haram-led suicide bombings and village raids continued this month. In a speech made during his visit to the United States, President Buhari criticised the U.S. decision to refuse weapon sales to Nigeria as part of the country's effort to defeat Boko Haram. On 7 July, Godwin Emefiele, the Governor of the Central Bank of Nigeria announced that Nigeria's external reserves had risen to $31.89 billion, allowing the country's economy to reposition itself ahead of its next phase of development. In response to Nigeria's decision to postpone its overdue devaluation of the naira, however, international investors have decided to avoid Nigeria's stock and bond markets, depressing the country's economy further. Some reports suggest that a less valuable currency is not necessarily harmful to Nigeria, as it could boost the country's oil exports.