AMSTERDAM—The Dutch state Friday nationalized troubled banking and insurance company SNS Reaal NV, following unsuccessful talks with private investors on a capital boost after heavy outflows of deposits had pushed the lender close to collapse in recent days.

The Dutch state will inject €2.2 billion ($2.99 billion) into the company, write off €800 million from an earlier bailout and €700 million on the value of SNS Reaal's toxic property loans. It will also provide an additional €6.1 billion in loans and guarantees to put the...