Obama came into office promising to talk to Iran without preconditions. The U.S. and Iran broke off diplomatic ties in 1979 after the Islamic revolution and the storming of the U.S. Embassy in Tehran, where dozens of Americans were held hostage for more than a year.
The June election of Iranian President Hassan Rouhani, a more moderate-sounding cleric, helped pave the way for a thaw in diplomatic relations with the U.S., a historic phone call between the two presidents and this latest round of nuclear negotiations.
Obama's outreach to Iran has worried Israel and Persian Gulf nations, which fear Iran is using the negotiations as a delay tactic while it continues to pursue a nuclear weapon.
The president said those nations "have good reason to be skeptical of Iran's intentions." But he said "only diplomacy can bring about a durable solution to the challenge posed by Iran's nuclear program."