ATLANTA — Georgia Gov. Brian Kemp on Tuesday signed into law one of the nation’s most restrictive abortion laws, a measure that bans the procedure once a fetal heartbeat is detected, which can be as early as six weeks, before many women know they are pregnant.

Kemp, a Republican, said he approved the bill “to ensure that all Georgians have the opportunity to live, grow, learn and prosper in our great state.”

The signing caps weeks of tension and protests at the state Capitol and begins what could be a lengthy and costly legal battle over the law’s constitutionality. But a legal showdown is exactly what supporters want.