Peace was gradually restored following a snap election in 1986 which consolidated PBS' position as the ruling state government. From 1990 to 1991, several PBS politicians were arrested under the Internal Security Act for allegedly being involved in plans to secede Sabah from the Malaysian Federation and detained for two years. Among those arrested were Jeffrey Kitingan and Maximus Ongkili. Other politicians, including Pairin, were hit with corruption charges. The arrests and charges were suspected to be politically motivated. Following the 1994 state election, Barisan Nasional regained control of the state via the creation of the Sabah chapter of the United Malays National Organisation (UMNO) party and other parties. The rotation system was introduced by the then prime minister Mahathir Mohamad in which the chief ministerial post would be rotated every two years among the three main communities in Sabah, namely, the Muslim Bumiputeras, non-Muslim Bumiputeras and the Chinese. Sakaran Dandai became the first chief minister under this system in 1994. The rotation system was finally abolished in 2005 with current chief minister Musa Aman at the helm. On 26 December 1996, Sabah was hit by one of the worst tropical storm known as Tropical Storm Greg. The storm hit the western coast of the state resulting in over 200 deaths and thousands of home destroyed. In 2000, the state capital Kota Kinabalu was granted city status, making it the 6th city in Malaysia and the first city in the state. Also this year, Kinabalu National Park was officially designated by UNESCO as a World Heritage Site, making it the first site in the country to be given such designation. On 3 May, the Abu Sayyaf militant group from southern Philippines arrived on the resort island of Sipadan and kidnapped 21 people consisting of tourists and resort workers for ransom. Most hostages were rescued on 16 September 2000 following an offensive by the Philippine army. In 2002, the International Court of Justice ruled that the islands of Ligitan and Sipadan, claimed by Indonesia, are part of Sabah and Malaysia. In early 2013, an armed group who identified themselves as the "Royal Sulu Army" intrude Sabah with the purpose of reclaiming the eastern areas as part of the defunct-Sultanate of Sulu. This resulted in a standoff and later in an armed conflict between the group and Malaysian security forces which ended with the death of 56 armed group followers and 10 Malaysian security forces along with 6 civilians. Soon, the state became the main targets of criminals and terrorists from the southern Philippines such as Abu Sayyaf and followers of the Moro National Liberation Front under Nur Misuari.