Beirut, Lebanon (CNN) -- In the latest spasm of violence in Lebanon over neighboring Syria's civil war, two suicide bombers blew themselves up outside the Iranian Embassy in southern Beirut on Tuesday.

At least 23 people died and 146 were injured, according to the Lebanese Health Ministry.

On Twitter, a radical Sunni group claimed responsibility for the attacks, saying similar assaults would continue until the Iran-supported Shiite group Hezbollah stops sending fighters to help Syrian government forces.

Hezbollah is based in Lebanon.

The Abdullah Azzam Brigades also demanded the release of its members being held prisoner in Lebanon.

Iran's cultural attache Sheikh Ibrahim Al-Ansari was at least gravely wounded in the attack.

Hezbollah TV reported that Al-Ansari was dead, citing the Iranian ambassador to Lebanon, but state-run Press TV cited the ambassador, Ghazanfar Roknabadi, as denying the attache was dead.

The state-run IRNA news agency reported Al-Ansari was in critical condition.

The dead also included two Iranian civilians who lived in a building close to the embassy, Lebanon's National News Agency reported.

The Lebanese army said one of the blasts was caused by a suicide bomber on a scooter, and the other was caused by a suicide bomber in an SUV.

Stunned witnesses looked on as massive flames and pillars of black smoke leaped into the the sky. The fires burned out several cars parked on a nearby street.

At least six buildings were damaged, Lebanese Internal Security Forces said.

Roknabadi said he had no doubt the embassy was the target of the two blasts, but he said any effort to thwart Iran's agendas would be unsuccessful.

"We have no fear when it comes to giving more martyrs in the line of duties," he told Hezbollah's Al-Manar TV.

IRNA quoted Foreign Ministry spokeswoman Marzieh Afkham as saying "Tehran will seriously follow up the criminal act with due consideration."

Lebanon's acting prime minister, Najib Mikati, said the blasts were "a cowardly terrorist attack" and urged the Lebanese public "to exercise the utmost restraint because we are going through a very difficult phase," Lebanon's state news agency NNA reported.

Mikati also called the Iranian ambassador to check on his safety and express his condolences, NNA said.

The United States declared the Abdullah Azzam Brigades a terrorist group in 2012, saying it was responsible for a 2010 attack on a Japanese-owned oil tanker in the Strait of Hormuz and had expressed interest in attacking Western interests in the Middle East.

The attack is the latest example of sectarian violence in Lebanon sparked by the Syrian conflict.

More than 100,000 people have died in Syria's ongoing civil war, which pits al-Assad's Alawite-dominated regime against largely Sunni rebel fighters seeking an end to his family dynasty. Alawites make up an offshoot of Shia Islam, but the majority of Syrians are Sunni.

In August, a pair of bombings ripped through neighborhoods near mosques in Tripoli, Lebanon, with ties to Syrian rebels. At least 27 people died.

Earlier in the month, a car bombing targeting a Hezbollah stronghold in a southern suburb of Beirut killed at least 22 and injured hundreds.

Lebanon also has been straining under the weight of more than 818,000 refugees from the Syrian conflict who have taken shelter there, according to the United Nations.

Group: 31 Syrian troops are killed in bomb attack

CNN's Nick Paton Walsh contributed to this report.

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http://www.cnn.com/2013/11/19/world/meast/lebanon-beirut-explosion/