Twin bomb blasts struck the southern Beirut area of Burj al-Barajneh on Thursday evening and killed at least 43 and injured more than 200, according to Sydney Morning Herald.

The Islamic State was quick to claim responsibility for the suicide bombings, one of the deadliest attacks in recent years in Lebanon.

The Islamic State group posted its claim of responsibility on social media pages linked to the Sunni militant group. “Soldiers of the caliphate blew themselves up in the stronghold of the heretics, and after the apostates crowded around the site of the explosion, a second martyr blew himself up using his explosive belt,” the statement read.

The group has vowed to carry out more attacks against Shiite areas.

The SMH also reported that the explosions hit around 6 PM in the stronghold of the Shi’ite group Hezbollah. The group has been fighting along with Syrian President Assad’s forces in Syria.

Speaking to the media from the scene, Health Minister of Lebanon, Wael Abou said many of those injured had severe injuries.

Prime Minister T. Salam, describing the attack as “cowardly criminal act”, announced a day of mourning for Friday. He also urged the Lebanese to unite.

U.N. Special Coordinator for Lebanon Sigrid Kaag also condemned the “heinous attack,” and said that the international community was standing by Lebanon.

At the scene of the blasts, residents showed the media what they said were metal pebbles that are usually put inside an explosive belt to inflict maximum casualties.

“They targeted civilians, worshippers, unarmed people, women and elderly, they only targeted innocent people,” Hezbollah official Bilal Farhat told The Associated Press, calling it a “satanic, terrorist attack.”

Hospitals in southern Beirut called on people to donate blood. They also appealed residents not to assemble at the entrance of medical establishments so that ambulances and emergency staff could work unhindered.

Hezbollah officials asked citizens to leave all cafés or restaurants in the area, which are usually full of customers on Thursday evenings and urged residents to inform the group about any suspicious activities.

Since the war began in 2011, an estimated 1.5 million Syrian refugees have fled across the border to Lebanon – they now make up a quarter of the country’s population – a country that is living through its own political crisis. The President’s chair has been lying empty for 17 months now.

More than 970 Hezbollah fighters have been killed in Syria, according to the Britain-based Syrian Observatory for Human Rights monitor.