What's the difference between the .ascii and the .string assembler directives?

I know that the .ascii directive doesn't put a null character at the end of the string. The .asciz directive is used for that purpose. However, I don't know whether the .string directive puts a null character at the end of the string. If it does, then what's the difference between the .asciz and the .string directives? To me, having both .ascii and .string seems redundant.