The Lebanese health minister said 146 more people were injured in the blasts.
Iranian Ambassador Ghazanfar Roknabadi said cultural attache Sheikh Ibrahim Ansari was among the dead. Speaking to Hezbollah's Al-Manar TV, he said Ansari took his post in Lebanon a month ago and was overseeing all regional cultural activities.
The blasts in south Beirut's neighborhood of Janah also caused extensive damage on the nearby buildings and the Iranian mission. The area is a stronghold of the militant Hezbollah group, which is a main ally of Syrian President Bashar Assad in the civil war next door. It's not clear if the blasts are related to Syria's civil war.
The neighborhood has been hit by several explosions in the past weeks that killed and wounded scores.
While suicide attacks are a frequent tactic for Hezbollah and Iran's sectarian rivals in al Qaeda and other Sunni extremist groups -- including the terror network's branch fighting alongside rebels in Syria -- Roknabadi blamed Israel for the attack in his interview with Al-Manar.
The Iranian Foreign Ministry in Tehran quickly followed suit, blaming the double bomb attack on terrorists "commissioned" by Israel.
The blasts came less than a week after Hezbollah leader Hassan Nasrallah showed up at a Shiite religious ceremony in southern Beirut and vowed to keep his fighters in Syria as long as needed to help Assad in the fight against the rebels.
"As long as there are reasons for us to stay in Syria, we will stay there," said the black-turbaned cleric, standing on an open-air podium, surrounded by several bodyguards.
Syria's civil war has pitted the mostly Sunni rebels against Assad's forces, dominated by his Alawite sect, a Shiite offshoot. Battle-hardened Hezbollah fighters openly joined the conflict earlier this year in a major boost to Assad and were instrumental in recent Syrian government victories, mostly in the suburbs of the Syrian capital of Damascus and in areas near the border with Lebanon.