In 1981, the new US President Ronald Reagan pursued a hard line approach to Libya, erroneously considering it a puppet regime of the Soviet Union. In turn, Gaddafi played up his commercial relationship with the Soviets, visiting Moscow again in April 1981 and 1985, and threatening to join the Warsaw Pact. The Soviets were nevertheless cautious of Gaddafi, seeing him as an unpredictable extremist. Beginning military exercises in the Gulf of Sirte – an area of sea that Libya claimed as a part of its territorial waters – in August 1981 the U.S. shot down two Libyan Su-22 planes monitoring them. Closing down Libya's embassy in Washington, D.C., Reagan advised U.S. companies operating in the country to reduce the number of American personnel stationed there. In March 1982, the U.S. implemented an embargo of Libyan oil, and in January 1986 ordered all U.S. companies to cease operating in the country, although several hundred workers remained. Diplomatic relations also broke down with the U.K., after Libyan diplomats were accused in the shooting death of Yvonne Fletcher, a British policewoman stationed outside their London embassy, in April 1984. In Spring 1986, the U.S. Navy again began performing exercises in the Gulf of Sirte; the Libyan military retaliated, but failed as the U.S. sank several Libyan ships.