Iran's supreme leader Ayatollah Ali Khamenei launched a fierce attack against regional rival Saudi Arabia, saying it was being pumped "like a milking cow" by "infidel" Americans.

"They (the Saudis) are close with the infidels and offer the enemy the money they should be using to improve the lives of their own people" Khamenei said at a meeting on Saturday

"But in reality there is no closeness and, as the Americans have said, they are just there to pump them for money like a milking cow, and later slaughter them," he added.

During a visit by President Donald Trump to Riyadh on May 21, Saudi Arabia agreed to buy $110 billion of US weapons and signed investment deals worth billions more.

Iran and the Gulf Arab states are backing opposing sides in the wars in Syria and Yemen, and the unrest in Bahrain. Relations were further hit last weekend when U.S. President Donald Trump visited Saudi Arabia and accused Tehran of supporting terrorism in the Middle East.