Mottaki also "expressed Iranian support" for Syria, an Iranian diplomat told AFP on condition of anonymity, saying "Iran denounced the deadly American assault" on October 26 that Damascus says killed eight civilians.
Mottaki delivered a message to Assad from Iranian President Mahmoud Ahmadinejad, Syria's state news agency SANA said. It covered the situation in Iraq, Lebanon and the Israeli-occupied Palestinian territories.
The foreign minister, whose country is Syria's key regional ally, later told reporters his visit was a sign of "the solidarity of the Iranian people with the Syrian people after the American raid."
On Friday, Ahmadinejad slammed the raid, launched across the border from a US base in Iraq, as a "savage act."
"The United States has committed a new error while carrying out this senseless and savage act," he was quoted as telling Assad in a telephone call.
Damascus says children were among eight civilians killed in the helicopter assault.
A US official in Washington has said the operation targeted a top militant who smuggled arms and fighters into Iraq but officially the State Department and Pentagon declined to comment.
Syria protested to the UN Security Council over what it branded a barbaric action, with the official press calling it a "cold-blooded war crime."
US commanders say Syria is the main transit point for foreign jihadists crossing into Iraq and have accused Damascus of turning a blind eye to the problem.
