In 1981, the new US President, Ronald Reagan, pursued a hard-line approach to Libya, claiming it to be a puppet regime of the Soviet Union. In turn, Gaddafi played up his commercial relationship with the Soviets, revisiting Moscow in 1981 and 1985, and threatening to join the Warsaw Pact. The Soviets were nevertheless cautious of Gaddafi, seeing him as an unpredictable extremist. In August 1981, the US staged military exercises in the Gulf of Sirte – an area which Libya claimed as a part of its territorial waters. The US shot down two Libyan Su-22 planes which were on an intercept course. Closing down Libya's embassy in Washington, DC, Reagan advised US companies operating in Libya to reduce the number of American personnel stationed there. In March 1982, the US implemented an embargo of Libyan oil, and in January 1986 ordered all US companies to cease operating in the country, although several hundred workers remained when the Libyan government doubled their pay. In Spring 1986, the US Navy again performed exercises in the Gulf of Sirte; the Libyan military retaliated, but failed as the US sank several Libyan ships. Diplomatic relations also broke down with the UK, after Libyan diplomats were accused in the killing of Yvonne Fletcher, a British policewoman stationed outside their London embassy, in April 1984.