Lebanon is holding a day of national mourning after at least 41 people were killed in two suicide bombings in the capital, Beirut. The Islamic State (IS) militant group says it was behind the attacks in Burj al-Barajneh, a mainly Shia southern suburb and Hezbollah stronghold. Hezbollah forces are fighting IS in neighboring Syria. The bombing is the deadliest in the capital since the end of Lebanon's civil war in 1990. Lebanese Prime Minister Tammam Salam called for unity in the face of attempts to create strife. In reaction from Washington, the White House in a statement condemned the "horrific terrorist" bomb blasts which it said "would only serve to reinforce our commitment to support the institutions of the Lebanese state, including the security services, to ensure a stable, sovereign and secure Lebanon". Iran - a key ally of Hezbollah - has also condemned the attack. The blasts on Thursday evening struck in a busy shopping street. More than 200 people were wounded - many of them seriously, Health Minister Wael Abou Faour said. The army said that two men wearing suicide vests carried out the attack. 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 bomber who failed to detonate his explosives was found at the scene of the second blast.