An al-Qaeda-linked group claimed responsibility for twin suicide bombings that struck outside the Iranian Embassy in Beirut on Tuesday, killing 23 people, including an Iranian diplomat, and wounding 146 others.

The obscure Abdullah Azzam Brigades said it carried out the mid-morning bombings in a southern Beirut Hezbollah stronghold — the latest strike in the proxy battles that have played out in the region for decades and now intensified with the civil war next door in Syria. The group is active in southern Lebanon and has issued claims in the past for rocket attacks into northern Israel.

The authenticity of the claim could not be independently verified but it was posted on a website and on the Twitter account of Sirajuddin Zurayqat, a prominent Islamic militant leader.

People fight outside [Lebanon], but send their messages through Lebanon. With bombs. It's their SMS service. - Explosion survivor

The group said it will continue with such attacks until the Iranian-backed Hezbollah group withdraws its forces from Syria, where the group is fighting alongside President Bashar al-Assad's forces against the Saudi Arabian-backed Sunni rebels seeking to topple him.

A Lebanese security official said the first suicide attacker was on a motorcycle that carried two kilograms of explosives. He blew himself up at the large black main gate of the Iranian mission, damaging the three-storey facility, the official said.

Less than two minutes later, a second suicide attacker driving a car rigged with 50 kilograms of explosives struck about 10 metres away, the official said. He spoke to The Associated Press on condition of anonymity in line with regulations.

Previous large-scale attacks on Hezbollah strongholds include an Aug. 15 car bombing in the southern Beirut suburbs that killed 27 people and wounded more than 300. A less powerful car bomb targeted the same area July 9, wounding more than 50.

Senior Hezbollah official Mahmoud Komati said at the scene that the attacks were a direct result of the "successive defeats suffered by (extremists) in Syria."

He described the blasts as a "message of blood and death" to Iran and Hezbollah for standing by Syria, vowing they would not alter their position.

Freelance reporter Rebecca Collard said from Beirut that the sound of the first explosion helped heighten the death toll.

"One of the saddest things I heard today was with that first explosion, many residents came to the balconies, to the windows of their neighbourhood, to see what had happened, only to be met with this much larger explosion, which ripped seven storeys high, ripping off balconies, smashing windows," she told CBC News Network.

Iranian Ambassador Ghazanfar Roknabadi identified the dead diplomat as Sheik Ibrahim Ansari. He said Ansari took his post in Lebanon a month ago and was overseeing all regional cultural activities. Hezbollah's Al-Manar TV reported that the street targeted by the suicide bombers includes a building where some of the Iranian diplomats and their families live.

Iran's Foreign Ministry blamed Israel in a phone conversation with his Lebanese counterpart, while Iranian President Hassan Rouhani blamed "extremists motivated by foreigners."

'People aren't sacred anymore'

At the scene, puddles of blood stained the ground, amid broken branches scattered from the blasts' force. A woman in a black robe and headscarf, unable to stand, clutched a man, pleading with security forces for help.

"Nader," she wailed, crying out a man's name. "Nader is missing." Another man ran from the area, carrying a South Asian migrant worker limp in his arms.

"People aren't sacred anymore. We aren't safe," said a mechanic whose store windows were shattered by the blasts. He declined to be identified because he did not want to be seen as involved in sectarian tensions that have split the Lebanese over Syria's conflict.

"People fight outside [Lebanon], but send their messages through Lebanon. With bombs. It's their SMS service," he added.

Debris was scattered on the street and cars were on fire as people ran away from the chaotic scene. AP video showed firefighters extinguishing flames from vehicles, blood-spattered streets and bodies covered with sheets on the ground. A charred motorcycle stood outside the embassy gate.