Phil Bryant, the Republican governor of Mississippi, on Thursday signed a bill largely banning abortions once doctors can detect a trace of a fetal heartbeat with an ultrasound, a milestone that can come as early as six weeks into pregnancy.

Mississippi is only the latest state to press for the strict abortion limit — the sort that has already been passed and then blocked in the courts in states including Kentucky, which approved it earlier this month, and Iowa, where a law passed last year was struck down by a state court in January. About 10 other states also are debating bills to ban abortions once fetal heartbeats are found, a point at which some women and girls are not yet aware that they are pregnant.

In a signing ceremony in Jackson on Thursday, Mr. Bryant described a heartbeat as “the universal hallmark of life since man’s very beginning.”

”We’re going to try to protect that child whenever we can,” said Mr. Bryant, who is barred by term limits from seeking another term as governor. “We think that this is showing the profound respect and desire of Mississippians to protect the sanctity of that very unborn life whenever possible.”