Two explosions outside the Iranian embassy in Lebanon's capital, Beirut, killed more than 20 people Tuesday, officials said.
A jihadist group claimed responsibility for what it said was a double suicide bombing intended to punish Iran for its allegiances in Syria.
The blasts occurred around 9:40 a.m., and caused smoke to billow from the embassy building in Beirut's southern Beir Hassan district, an eyewitness told NBC News.
Lebanon's health ministry said at least 23 people were killed and 146 injured, according to Agence France-Presse.
US Secretary of State John Kerry strongly condemned the "senseless and despicable terrorist bombings" at the embassy, offering condolences and calling for restraint in a statement Tuesday.
British Prime Minister offered condolences to Iran's prime minister in the first call between British and Iranian leaders in over a decade. While speaking with Prime Minister Hassan Rouhani, Cameron talked about "all of us taking a firm stand against terrorism," according to a Downing Street spokeswoman.
The Associated Press cited an Iranian security guard who said a suicide bomber approached the embassy gate and blew himself up. Then, the guard said, a second attacker detonated an even more powerful car bomb.
The Abdullah Azzam Brigades, an Islamist militant group with ties to Al Qaeda, claimed responsibility for the attack, Reuters reported, citing Twitter posts from one of the movement's leading members.
"It was a double martyrdom operation by two of the Sunni heroes of Lebanon," wrote the group's spiritual guide, Sheikh Sirajeddine Zuraiqat. He said that more attacks would follow for as long as Iran continued to support President Bashar al-Assad's government in Syria.
Iran is known to back Lebanon-based Hezbollah, which has sent its fighters to assist the regime's forces against their armed opponents.
Southern Beirut, which is predominantly Shia, is considered a stronghold of Hezbollah, according to the AP. Several bomb and rocket attacks have been reported there in recent months — retaliation, Syrian rebels have claimed, for Hezbollah's involvement in Syria.
"The aim of the blast is to stir up the situation in Lebanon and use the Lebanese arena to convey messages," Lebanese Prime Minister Najib Mikati told local media, according to the BBC.
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