A view shows Horizon Park business centre in Kiev, Ukraine, August 18, 2016. REUTERS/Valentyn Ogirenko

Traditional flutists perform to welcome US Secretary of State John Kerry at the palace of the Sultan of Sokoto on August 23, 2016 in Sokoto. Kerry congratulated Nigeria on its recent military successes against Boko Haram, but warned the country will face a blowback if it "cracks down" on the Islamists with excessive force. The top US diplomat, who was in Kenya on August 22, is expected to discuss the Boko Haram insurgency, fighting corruption and boosting Nigeria's moribund economy that has been pummelled by the drop in global oil prices. / AFP PHOTO / PIUS UTOMI EKPEIPIUS UTOMI EKPEI/AFP/Getty Images

Traditional flutists perform to welcome US Secretary of State John Kerry at the palace of the Sultan of Sokoto on August 23, 2016 in Sokoto. Kerry congratulated Nigeria on its recent military successes against Boko Haram, but warned the country will face a blowback if it "cracks down" on the Islamists with excessive force. The top US diplomat, who was in Kenya on August 22, is expected to discuss the Boko Haram insurgency, fighting corruption and boosting Nigeria's moribund economy that has been pummelled by the drop in global oil prices. / AFP PHOTO / PIUS UTOMI EKPEIPIUS UTOMI EKPEI/AFP/Getty Images

Traditional flutists perform to welcome US Secretary of State John Kerry at the palace of the Sultan of Sokoto on August 23, 2016 in Sokoto. Kerry congratulated Nigeria on its recent military successes against Boko Haram, but warned the country will face a blowback if it "cracks down" on the Islamists with excessive force. The top US diplomat, who was in Kenya on August 22, is expected to discuss the Boko Haram insurgency, fighting corruption and boosting Nigeria's moribund economy that has been pummelled by the drop in global oil prices. / AFP PHOTO / PIUS UTOMI EKPEIPIUS UTOMI EKPEI/AFP/Getty Images

Traditional flutists perform to welcome US Secretary of State John Kerry at the palace of the Sultan of Sokoto on August 23, 2016 in Sokoto. Kerry congratulated Nigeria on its recent military successes against Boko Haram, but warned the country will face a blowback if it "cracks down" on the Islamists with excessive force. The top US diplomat, who was in Kenya on August 22, is expected to discuss the Boko Haram insurgency, fighting corruption and boosting Nigeria's moribund economy that has been pummelled by the drop in global oil prices. / AFP PHOTO / PIUS UTOMI EKPEIPIUS UTOMI EKPEI/AFP/Getty Images

Sokoto Sultan and President-General of the Nigerian National Supreme Council for Islamic Affairs (NSCIA) Muhammad Sa'ad Abubakar stands during a meeting with US Secretary of State the Palace of the Sultan in Sokoto, on August 23, 2016. John Kerry congratulated Nigeria on its recent military successes against Boko Haram, but warned the country will face a blowback if it "cracks down" on the Islamists with excessive force. The top US diplomat, who was in Kenya on August 22, is expected to discuss the Boko Haram insurgency, fighting corruption and boosting Nigeria's moribund economy that has been pummelled by the drop in global oil prices. / AFP PHOTO / PIUS UTOMI EKPEIPIUS UTOMI EKPEI/AFP/Getty Images

US Secretary of State John Kerry (R) speaks with Sokoto Sultan and President-General of the Nigerian National Supreme Council for Islamic Affairs (NSCIA) Muhammad Sa'ad Abubakar (R) outside the Palace of the Sultan in Sokoto, on August 23, 2016. Kerry congratulated Nigeria on its recent military successes against Boko Haram, but warned the country will face a blowback if it "cracks down" on the Islamists with excessive force. The top US diplomat, who was in Kenya on August 22, is expected to discuss the Boko Haram insurgency, fighting corruption and boosting Nigeria's moribund economy that has been pummelled by the drop in global oil prices. / AFP PHOTO / PIUS UTOMI EKPEIPIUS UTOMI EKPEI/AFP/Getty Images

US Secretary of State John Kerry delivers a speech at the Palace of the Sultan in Sokoto, on August 23, 2016. Kerry congratulated Nigeria on its recent military successes against Boko Haram, but warned the country will face a blowback if it "cracks down" on the Islamists with excessive force. The top US diplomat, who was in Kenya on August 22, is expected to discuss the Boko Haram insurgency, fighting corruption and boosting Nigeria's moribund economy that has been pummelled by the drop in global oil prices. / AFP PHOTO / PIUS UTOMI EKPEIPIUS UTOMI EKPEI/AFP/Getty Images