Mortar shells crashed into an Iraqi prison at a major government complex Monday, landing in a cellblock and killing at least five inmates. Elsewhere, an explosive fire erupted in a storage tank at Baghdad's only oil refinery, sending smoke and flames high above the capital. The US military said an "industrial accident" caused the fire at the Dora refinery in Baghdad. But the chief Iraqi military spokesman, Brig. Qassim al-Moussawi, told The Associated Press that a rocket struck a storage tank, triggering the blaze. The attack on the prison was part of an increase in violent incidents throughout the city over the past few days, which have included mortar or rocket fire on the US-controlled Green Zone. Also Monday, a suicide car bomber killed one US soldier was killed and wounded two others in Salahuddin province, a mostly Sunni area north of Baghdad, the military said.