"The US has more than 12,000 nuclear weapons, the [former] Soviet Union has about the same; Great Britain and France have several hundred, and Israel has 150 or more," Carter said, according to a transcript of his remarks published by the festival.
"We have a phalanx of enormous weaponry ... not only of enormous weaponry but of rockets to deliver those missiles on a pinpoint accuracy target."
Carter also said that the US government should talk directly to Iran in order to persuade it to drop its nuclear ambitions.
The US and other Western powers have accused Tehran of attempting to acquire nuclear weapons however Iran says its nuclear programme is purely for peaceful purposes.
His remarks come after the former US president caused controversy by holding talks with Khaled Meshaal, leader of the Palestinian movement Hamas, in Damascus, the Syrian capital, in April.
The meeting led to criticism from Israel and the Bush administration.
Hamas is listed as a terrorist organisation by the US, Israel and the European Union, and has not been invited to participate in US-brokered peace negotiations between Israel and the Palestinians.
Experts have long maintained that Israel is the Middle East's only nuclear power, however the country has refused to confirm or deny the claim.
Most estimates for the number of weapons are based on evidence leaked to the media by Mordechai Vanunu, an Israeli former nuclear technician, who said the Jewish state had between 100 and 200 weapons.
Vanunu spent 18 years in an Israeli prison for disclosing nuclear secrets before being released in 2004.
Other experts have said the number is as low as 60 or as high as 400.
It is not clear what evidence or intelligence Carter was basing his information on.