The United States was the largest seller of arms to Iran under Mohammad Reza Pahlavi, and the vast majority of the weapons that the Islamic Republic of Iran inherited in January 1979 were American-made. To maintain this arsenal, Iran required a steady supply of spare parts to replace those broken and worn out. After Iranian students stormed the American embassy in Tehran in November 1979 and took 52 Americans hostage, U.S. President Jimmy Carter imposed an arms embargo on Iran. After Iraq invaded Iran in September 1980, Iran desperately needed weapons and spare parts for its current weapons. After Ronald Reagan took office as President on 20 January 1981, he vowed to continue Carter's policy of blocking arms sales to Iran on the grounds that Iran supported terrorism.