Set up in May 1948, the United Nations Truce Supervision Organization (UNTSO) was the first ever peacekeeping operation established by the United Nations. Since then, UNTSO military observers have remained in the Middle East to monitor ceasefires, supervise armistice agreements, prevent isolated incidents from escalating and assist other UN peacekeeping operations in the region to fulfil their respective mandates.
More Information: https://peacekeeping.un.org/en/mission/untso