BAGHDAD — Insurgents launched a wave of attacks across Iraq on Monday, primarily targeting Shi’ite communities and pilgrims and killing at least 23 civilians and five police officers, authorities said.

The attacks appeared aimed at undermining security and confidence in the government by fomenting sectarian conflict. Overall violence has dropped since the nation neared a civil war several years ago, but attacks of a sectarian nature come almost daily, and government forces seem powerless to prevent them.