Lebanese security forces have arrested nine people, most of them Syrian nationals, over last week's twin bombings in Beirut that killed 44 people.
The interior minister says the detained include seven Syrians and two Lebanese, one of them a would-be suicide bomber and the other a trafficker who smuggled them across the border from Syria.
The Islamic State jihadist group claimed responsibility for Thursday's attacks, which hit a busy shopping street in Burj al-Barajneh, a suburb where the Shi'ite movement Hezbollah is popular.
"Within 24 hours the network was arrested in the fastest uncovering of a bombing incident in the country," a security source said.
The explosions were the first attacks in more than a year to target a Hezbollah stronghold in Lebanon, as the Iran-backed group steps up its involvement in the war in neighbouring Syria.
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Lebanon's Hezbollah leader Sayyed Hassan Nasrallah said Syrian and Lebanese detainees were arrested on suspicion of being involved in the bombings, which he squarely blamed on Islamic State. However, he did not say if any of those arrested were Palestinian.
Nasrallah warned his followers of a backlash against ordinary Syrians and Palestinians in the aftermath of the bombings, saying the goal of radical Islamist Sunni fundamentalists, who consider Shi'ites to be heretics, was to sow discord among Sunnis and Shi'ites.
The blasts occurred almost simultaneously late on Thursday and struck a Shi'ite community centre and a nearby bakery in the commercial and residential area of Borj al-Barajneh, security sources said. A closely guarded Hezbollah-run hospital is also nearby.
