Although Kuwait formally gained independence in 1961, Iraq initially refused to recognize the country's independence by maintaining that Kuwait is part of Iraq, albeit Iraq later briefly backed down following a show of force by Britain and Arab League support of Kuwait's independence. The short-lived Operation Vantage crisis evolved in July 1961, as the Iraqi government threatened to invade Kuwait and the invasion was finally averted following plans by the Arab League to form an international Arab force against the potential Iraqi invasion of Kuwait. As a result of Operation Vantage, the Arab League took over the border security of Kuwait and the British had withdrawn their forces by 19 October. Iraqi prime minister Abd al-Karim Qasim was killed in a coup in 1963 but, although Iraq recognised Kuwaiti independence and the military threat was perceived to be reduced, Britain continued to monitor the situation and kept forces available to protect Kuwait until 1971. There had been no Iraqi military action against Kuwait at the time: this was attributed to the political and military situation within Iraq which continued to be unstable. A treaty of friendship between Iraq and Kuwait was signed in 1963 by which Iraq recognised the 1932 border of Kuwait. The Kuwait-Iraq 1973 Sanita border skirmish evolved on 20 March 1973, when Iraqi army units occupied El-Samitah near the Kuwaiti border, which evoked an international crisis.