In 1990, the PLA sent five military observers to the UN Truce Supervision Organization (UNTSO) - the first time China had taken part in UN peacekeeping missions. In 1992, it dispatched an engineering corps of 400 officers and men to the UN Transitional Authority in Cambodia (UNTAC) - the first time China had sent an organic military unit on a peacekeeping mission. To date, the PLA has dispatched 22,000 military personnel to 23 UN peacekeeping missions. All of them have been awarded the UN peace medals. Three officers and six soldiers have laid down their lives performing such duties and were posthumously awarded the Dag Hammarskjold medal. So far, China is the biggest troop and police contributor among the five permanent members of the UN Security Council. It also dispatches the most numbers of troops for engineering, transportation and medical support among all the 115 contributing countries. China pays and contributes the largest share of UN peacekeeping costs among all developing countries.