LAGOS, March 22 (Reuters) - Robbers have killed four police and raided six banks in southeast Nigeria, police said on Thursday -- the latest incident in a pre-election crime wave.

The officers were on patrol in Obosi town in the state of Anambra on Wednesday when they were shot dead by a gang of about 40 robbers, a police spokesman said.

The robbers later raided banks in the town of Nnewi, 20 miles (30 km) away, and stole an undisclosed amount of cash, he added.

Anambra has witnessed a dramatic surge in violent crime and kidnappings in the run-up to general elections in April, which should mark the first transition from one democratic government to another since Nigeria's independence from Britain in 1960.

Robberies and other crimes normally grow around elections in Nigeria because politicians arm local militias and long-standing communal grievances are exacerbated by the prospect of power changing hands.

Political tensions are particularly high in Anambra state because the electoral body ruled last week that the names of three leading opposition candidates would not appear on the ballot.

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