Indonesia's President Joko Widodo sits in the cockpit of a Sukhoi fighter jet while attending a military exercise at Ranai military airbase in Natuna Island, Riau Islands province, Indonesia October 6, 2016. President Joko Widodo watched from Ranai, capital of the Natuna Islands archipelago, with hundreds of military officials as about 70 jets carried out manoeuvres that included a dog fight and dropping bombs on targets off the coast. REUTERS/Beawiharta

Indonesia's President Joko Widodo (C) along with Military Chief Gatot Nurmantyo (L) and Airforce Comander Agus Supriatna walk past fighter jets and weapons during a military exercise on Natuna Island, Riau Islands province, Indonesia October 6, 2016. Indonesian officials described Widodo's visit at that time as a strong message to Beijing following a spate of face-offs between Indonesia's navy and Chinese fishing boats in the gas-rich southern end of the South China Sea. REUTERS/Beawiharta

Indonesia's President Joko Widodo smiles as he sits in the cockpit of a Sukhoi fighter as Military Chief Gatot Nurmantyo and Airforce Commander Agus Supriatna look on while attending a military exercise at Ranai military airbase on Natuna Island, Riau Islands province, Indonesia October 6, 2016. President Joko Widodo watched from Ranai, capital of the Natuna Islands archipelago, with hundreds of military officials as about 70 jets carried out manoeuvres that included a dog fight and dropping bombs on targets off the coast. REUTERS/Beawiharta

A Sukhoi fighter jet is seen during a military exercise at Ranai military airbase in Natuna Island, Riau Islands province, Indonesia October 6, 2016. Indonesian warplanes on Thursday staged a large-scale exercise on the edge of South China Sea territory claimed by Beijing, a show of force that adds to regional uncertainty sparked by the Philippines' sudden tilt away from the United States. REUTERS/Beawiharta

Indonesia soldiers jump from a Hercules C-130 military transport plane during an exercise at Ranai military airbase in Natuna Island, Riau Islands province, Indonesia October 6, 2016. Indonesian officials described Widodo's visit at that time as a strong message to Beijing following a spate of face-offs between Indonesia's navy and Chinese fishing boats in the gas-rich southern end of the South China Sea. REUTERS/Beawiharta

Indonesia soldiers jump with parachutes from a Hercules C-130 military transport plane during an exercise at Ranai military airbase in Natuna Island, Riau Islands province, Indonesia October 6, 2016. Indonesian warplanes on Thursday staged a large-scale exercise on the edge of South China Sea territory claimed by Beijing, a show of force that adds to regional uncertainty sparked by the Philippines' sudden tilt away from the United States. REUTERS/Beawiharta