At least 37 people have been killed and 181 wounded in two suicide bomb attacks in a residential area of the Lebanese capital, Beirut, officials say.
The bombers blew themselves up in a busy street in the southern suburb of Burj al-Barajneh, a stronghold of the Shia Islamist Hezbollah movement.
The Sunni jihadist group Islamic State (IS) claimed responsibility, but there has been no independent confirmation.
It is the deadliest bombing in Beirut since the civil war ended 25 years ago.
Prime Minister Tammam Salam condemned the attacks as "unjustifiable" and called on Lebanon's rival factions to unite against "plans to create strife".
Two bombers blew themselves up a short distance from each other in a street in Burj al-Barajneh at around 18:00 local time (16:00 GMT).
One security source told the Associated Press that the first bomber detonated his explosive vest outside a Shia mosque, while the second blew himself up inside a nearby bakery.
The body of a third suicide bomber was found nearby. He was apparently killed by the second blast before he could detonate his own explosive vest.
"I'd just arrived at the shops when the blast went off. I carried four bodies with my own hands, three women and a man, a friend of mine," one witness told a local television station.
Another said: "When the second blast went off, I thought the world had ended."
IS subsequently issued a statement saying that it was behind the bombings. It identified the three attackers as two Palestinians and a Syrian.
Hezbollah vowed to continue its fight against "terrorists", warning of a "long war" against its enemies, according to the Reuters news agency.
"They targeted civilians, worshippers, women and the elderly. It only targeted those innocent people. This is a Satanic terrorist act, carried out by apostates," Hezbollah MP Bilal Farhat told AP.
The group's strongholds in southern Beirut were the target of a series of bombings in 2013 and 2014 mostly claimed by Sunni jihadist militants -who denounced Hezbollah's decision to send fighters to neighbouring Syria to prop up President Bashar al-Assad.
In recent weeks, Hezbollah has sent reinforcements to Syria in support of government offensives in northern areas held by rebel forces or IS.
BBC Arab affairs analyst Sebastian Usher says it is no surprise that IS has claimed these bombings, but the ferocity will once again reawaken the spectre of Lebanon's 15-year civil war.
So far the country - locked in political stalemate and with a crisis over uncollected rubbish having mobilised mass protests in the summer - has managed to hold onto its fragile stability, he adds.