BEIRUT - The Lebanese army said Saturday it had arrested five Syrian men found with explosives and suspected of planning an attack on a Shi'ite Muslim procession Sunday.

The war in neighboring Syria, pitting majority Sunni Muslim rebels against President Bashar Assad's inner circle of Alawites - an offshoot of Shi'ite Islam - has widened rifts in Lebanon, still politically divided along sectarian lines deepened by its own 15-year civil war.

Shi'ite Hezbollah has sided with Assad, and anger is growing among Sunnis and other groups sympathetic to the Syrian opposition.

The arrests, in the southern town of Nabatieh, followed an army raid on a house where 450 grams of explosives were discovered, the army said. The men were believed to have been planning to attack a procession in the town to mark the Shi'ite festival of Ashura.

"The five Syrians have been living in Lebanon for years. They are thought to have been planning an attack on Shi'ites," a source said, on condition of anonymity.

Shi'ites across the country hold rallies during Ashura, but Nabatieh is one of the few places where Shi'ites observe the tradition of drawing blood by self-flagellation.

Ashura marks the killing of Imam Hussein ibn Ali, grandson of the Prophet Mohammed, at the battle of Karbala in Iraq in 680 - the culmination of a power struggle that ushered in the Sunni-Shi'ite divide which still shapes the Middle East's political map today.