Negotiations for START I began in May 1982, but continued negotiation of the START process was delayed several times because US agreement terms were considered non-negotiable by pre-Gorbachev Soviet rulers. Reagan's introduction of the Strategic Defense Initiative (SDI) program in 1983 was viewed as a threat by the Soviets, who withdrew from setting a timetable for further negotiations. In January 1985, however, US Secretary of State George Shultz and Soviet Foreign Minister Andrei Gromyko discussed a formula for a three-part negotiation strategy that included intermediate-range forces, strategic defense, and missile defense. During the Reykjavík Summit between Reagan and Gorbachev in October 1986, negotiations towards the implementation of the START Program were accelerated and turned towards the reduction of strategic weapons after the Intermediate-Range Nuclear Forces Treaty was signed in December 1987.