KABUL (Reuters) - Defense Secretary Leon Panetta arrived in Kabul on Tuesday for an unannounced visit, as the United States and its Western allies reduce troop levels in Afghanistan despite persistent violence.

Panetta visits Afghanistan on the heels of bomb attacks last week on Shi'ite Muslim ceremonies in three cities across the country, that Afghan President Hamid Karzai said killed 80 people.

(Reporting by Missy Ryan, editing by Dan Magnowski)