Louisiana's Democratic governor has signed a highly restrictive new abortion law that bans the procedure after a foetal heartbeat is detected.

The law could prohibit abortions as early as six weeks into pregnancy.

State legislators overwhelmingly backed the bill on Wednesday, by 79 votes to 23 and Governor John Bel Edwards signed the bill into law on Thursday.

It is the latest in a raft of anti-abortion measures which are expected to face legal challenges.

Four other states have passed similar limits to abortion this year.