Rouhani's remarks followed a phone call to his Lebanese counterpart the previous day, in which the Iranian president pledged Tehran's support for Lebanon's stability following the resignation of the Saudi-backed Prime Minister Saad Hariri.
The surprise resignation, announced on TV from Saudi Arabia, threw the Lebanese government into disarray and exposed a new front for the tensions between the Sunni powerhouse and its archrival Shiite-led Iran.
According to Rouhani's official website, the Iranian president said that "there is no case in history that a country forces another one's authority to resign only to interfere (in) their internal affairs."
"Why are you interfering with Lebanon's internal affairs and governance," Rouhani said, addressing Saudi Arabia. "This is an unprecedented event in history."
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Hariri unexpectedly announced he was resigning on Saturday and accused Iran of meddling in Arab affairs and the Iran-backed Lebanese militant group Hezbollah of holding Lebanon hostage. Hezbollah has members in the Lebanese unity government that Hariri formed last year.
Iranian officials called the resignation a "plot" by the United States, Israel and the Saudis to foment tensions in Lebanon and the region.
Casting himself as the voice of reason, Rouhani also questioned the benefits of Saudi Arabia's "hostility toward the peoples of the region" and urged the kingdom to choose "friendship" instead.
"You are making mistake if you think Iran is not your friend and the US and Israel are your friends," Rouhani also said, according to the semi-official ISNA news agency. "This is a strategic miscalculation."
In his call to Aoun late Tuesday, Rouhani said Iran firmly believes the Lebanese people will overcome "this sedition" and "will not allow Lebanon to become a battlefield for foreign powers and an opportunity for the terrorists to re-emerge."
According to Rouhani's website, Aoun told him that Lebanon is going through a "difficult" situation but that peace is still in place despite "some very weak voices that want to create tensions."
"Our relationship with the government will not change," US State Department spokeswoman Heather Nauert told reporters yesterday.
She added that Washington considers Hezbollah a terrorist organization. Washington has recently imposed new sanctions on the Shiite group, including a bounty on two of Hezbollah's senior military commanders.
"The United States strongly supports the legitimate institutions in the Lebanese state. We expect all members of the international community to respect those institutions and the sovereignty and the political independence of Lebanon," Nauert said.