Mississippi's governor has just signed into law the tightest abortion restrictions in the US.

The bill bans most abortions after 15 weeks, with no exceptions for rape or incest.

The only exemptions are in cases where there is a foetal abnormality that is "incompatible with life", or the mother's life is in danger.

Mississippi previously banned abortions from 20 weeks. Critics say the new law is unconstitutional.

The measure was enacted on Monday by Republican Governor Phil Bryant, who says he wants the southern state to be "the safest place in America for an unborn child".

The Center for Reproductive Rights said it had filed a lawsuit to block the new law on behalf of the only abortion clinic in Mississippi, the Jackson Women's Health Organization.

Diane Derzis, who runs that clinic, said earlier this month that anti-abortion activists were seeking to undermine Roe v Wade, the landmark 1973 US Supreme Court case which legalised abortion.

She told the Clarion-Ledger newspaper: "These groups are tossing anything and everything out there, anything that could start winding its way through the legal system because we're in a very fragile place right now."

In 2014 federal judges ruled that attempts for six- and 12-week bans in North Dakota and Arkansas were unconstitutional, and struck them down.

President Trump has supported a proposed federal ban on abortions after 20 weeks after fertilisation, but the bill was blocked in the Senate in January.