Iran is Opec's second largest oil exporter
"The oil belongs to the people and can be a weapon against the West and those countries who support the savage regime of Israel," Mr Khamenei said in a sermon during Friday prayers in Tehran.
Mr Khamenei said that exports should be stopped "for a symbolic period of one month."
Iran is the second largest exporter of oil from the Middle East and a member of the Opec producers' cartel.
The news initially sent crude oil futures soaring back above $27 a barrel, but by the end of the day, prices had fallen back to close at $26 a barrel.
An Opec rejection of Iran's call also lifted sentiment.
One Opec official said that an export suspension would work to the benefit of non-Opec countries such as Russia, who could raise production to fill the supply gap.
Oil shock
Iraq has previously called for such an embargo, but Saudi Arabia and Kuwait both rejected the idea.
On Thursday, Opec - whose members produce 40% of the world's crude supply - insisted it would not use oil as an economic weapon.
Iran is an important member of the cartel but is generally not thought to have as much influence as Saudi Arabia.
Mr Khamanei said that the success of such a scheme would depend on the co-operation of all oil-producing countries in the Middle East.
"If they [the Western countries] do not receive oil their factories will come to a halt. This will shake the world," he said, evoking memories of the 1973 oil crisis.
A 1973 embargo by Opec members caused a severe oil shock and widespread economic chaos around the world.
Violence premium
Oil prices have been moving steadily higher since February due to the escalating violence in the Middle East.
The region supplies about 30% of the world's demand for oil and prices react to fears that the political situation could hamper supply.
High crude oil prices tend to feed through to petrol prices at the pump in the West since refiners are forced to pay more for their oil.