While Beirut has endured such attacks periodically, the assault shattered a relative calm that had prevailed in recent months. It also showed Lebanon’s vulnerability to the vindictive wrath of the Islamic State.
The Lebanese Army said in a statement that the bombers had struck at 6 p.m., during the evening rush hour, apparently to maximize casualties. The army said that the body of a third bomber had been found near one of the blast sites but that his explosives belt was still largely intact.
The attack took place in the Bourj al-Barajneh neighborhood of southern Beirut, an area that includes a Palestinian refugee camp and that has absorbed many Syrian refugees.
It is a bustling area with narrow streets, many small shops and vendors selling fruits and vegetables from stalls and pushcarts. Television stations broadcast images of people carrying the wounded away from flaming rubble. The blasts went off near a bakery, and just yards from a hospital.
The Health Ministry said that by evening, the death toll had reached at least 43, with 239 wounded. Al Manar, Hezbollah’s news website, said children were among the victims.
It was the second time in two weeks that the Islamic State, also known as ISIS or ISIL, claimed to have struck, through civilian targets, the countries and groups fighting it in Syria. The Islamic State’s Egyptian affiliate claimed responsibility for the Oct. 31 destruction of a jetliner full of Russian vacationers from the Sinai Peninsula in Egypt.
Russia, along with Hezbollah and Iran, is a crucial ally of the Syrian government and says it is fighting the Islamic State in Syria. Talks are set to begin this weekend in Vienna in a renewed international effort to find a political solution to the Syria conflict, now in its fifth year.
Thursday was also punctuated by new offensives in Syria and Iraq against the Islamic State. American-backed Kurdish forces are confronting the group in both Iraq and Syria; at the same time, the Syrian government, Hezbollah and other allied forces have made advances against the Islamic State.
Hussein Khalil, a political aide to the leader of Hezbollah, Hassan Nasrallah, visited the scene and called the attackers “beasts,” according to local news reports. Lebanon’s prime minister, Tammam Salam, also condemned the bombings. The government declared Friday a day of national mourning and announced that schools would be closed.
The American Embassy in Beirut issued a statement saying that the United States “strongly condemns heinous attack” and that officials extended “condolences to victims’ families, wish speedy recovery to wounded.”
Since the Syrian civil war erupted in 2011, Beirut and other Lebanese cities have been subjected to bombings and other attacks carried out in the name of rival Syrian factions. Hezbollah, an influential political power in Lebanon that is regarded by Israel and the United States as a terrorist organization, has sent thousands of fighters to provide pivotal support to the Syrian president, Bashar al-Assad.
While Hezbollah and the United States are nominally both fighting the Islamic State, they remain deeply at odds and carry on their military campaigns separately. American officials say the Syrian government, backed by Russia, Hezbollah and Iran, is primarily targeting Mr. Assad’s other opponents and not the Islamic State. The pro-Assad alliance says the United States is not serious about fighting the Islamic State.
A double bombing last year near an Iranian cultural center in the Hezbollah enclave killed at least five people and wounded dozens. An offshoot of Al Qaeda claimed responsibility for that attack and said it would carry out more bombings against Hezbollah until the group withdrew its fighters from Syria.
The attack on Thursday appeared to be the worst in terms of casualties since Aug. 23, 2013, when bombs hit two mosques in the northern Lebanese city of Tripoli, killing at least 42 people and wounding hundreds.