Fires engulfed cars outside the embassy and the facades of some buildings were torn off. Shattered glass covered the bloodied streets and some trees were uprooted, but the embassy's well-fortified building itself suffered relatively minor damage.

"Whoever carries out such an attack in these sensitive circumstances, from whichever faction, knows directly or indirectly that he is serving the interests of the Zionist entity (Israel)," Roknabadi said.

Burnt cars at the site of explosions near the Iranian embassy in Beirut November 19, 2013. Two explosions, at least one caused by a suicide bomber, rocked Iran's embassy in Lebanon on Tuesday, killing at least 23 people, including an Iranian cultural attache, and hurling bodies, cars and debris across the street. [Photo/Xinhua]

He did not say whether other embassy officials were among the dead, but Lebanese TV stations quoted Iranian diplomatic sources as saying none of their staff in the embassy was hurt.

UK ENVOY GIVES BLOOD

In a sign of the tentative thaw in Western relations with Iran following the election of President Hassan Rouhani, France and Britain both went beyond standard condemnations of the bloodshed in their public responses.

Paris expressed "solidarity with the Lebanese and Iranian authorities", while British ambassador to Beirut Tom Fletcher donated blood in a move his embassy described on Twitter as "solidarity for injured in terrorist attack on Iranian embassy".

In Washington, the White House condemned the bombings and called on all sides in Lebanon to exercise calm and restraint.

Politicians from across Lebanon's Sunni, Shi'ite and Christian communities also condemned the attack.

In Syria, the government said its soldiers took full control of the town of Qara, which straddles a highway from Damascus to government strongholds on the coast and is also used by Sunni rebels to cross into Syria from Lebanon.

The capture of Qara may mark the start of a wider offensive by the army, which has been backed by Hezbollah and Shi'ite fighters from Iraq, to recapture the mountainous border region of Qalamoun and consolidate Assad's control of territory around Damascus and close to the Lebanese border.

Hezbollah's military role in Syria has helped to inflame sectarian tension there and in Lebanon. Many Lebanese Sunnis back the Syrian rebels, while many Shi'ites support Assad, whose minority Alawite sect derives from Shi'ite Islam.

Ayham Kamel, Middle East analyst with Eurasia Group, said the embassy bombing was an attempt by supporters of the Sunni rebels to weaken Hezbollah and Iran's support for Assad, undermine the Qalamoun campaign and possibly pressure Tehran before Wednesday's nuclear talks.

"While sectarian tensions in Lebanon will increase, Hezbollah's retaliatory response will be centred on Syria where (it) will further commit military forces to eliminate the Sunni rebel threat along the Syrian-Lebanese borders," he said.

The Abdullah Azzam Brigade has strong links in Lebanon's Palestinian refugee camps as well as connections with the Gulf. Two of its senior military leaders are Saudi nationals, said Charles Lister, an analyst at IHS Jane's Terrorism and Insurgency Centre.

"This attack is a significant escalation. After months and months of speculation, an al Qaeda-linked group has now underlined its involvement in the Syria-related Lebanese theatre," he said.

Syrian Information Minister Omran Zoabi implicitly blamed Saudi Arabia and Qatar for supporting radical militants, who have been blamed for previous attacks against Shi'ite targets.

Footage from local news channels showed charred bodies on the ground as flames rose from stricken vehicles. Emergency workers and residents carried victims away in blankets.

"These kinds of explosions are a new and dangerous development," said the head of Hezbollah's parliamentary bloc in Lebanon, Mohammad Raad.

Southern Beirut, a Hezbollah stronghold, was hit by three explosions earlier this year. Those attacks were blamed on groups linked to the Syrian rebels, believed to be in retaliation for the group's military role in Syria.

Three decades ago, Iranian-backed Shi'ite militants carried out devastating suicide bombings in Lebanon that hit the US embassy, as well as US., French and Israeli military bases.