The US Department of Justice has filed a civil lawsuit challenging Texas' controversial abortion law.

"The act is clearly unconstitutional," Attorney General Merrick Garland said at a briefing on Thursday.

It bans abortions from as early as six weeks into pregnancy and allows anyone to sue those involved in the procedure.

Doctors and women's rights groups have strongly condemned the law, which took effect last week after the Supreme Court failed to block it.

SB8, also known as the Texas Heartbeat Act, came into effect last week after the Supreme Court did not respond to an emergency appeal filed by abortion providers.

In an unsigned opinion, the court said that although the appeals had raised "serious questions" about the constitutionality of the law, it could not block it due to complex and "novel" procedural questions.

The lawsuit says: "It takes little imagination to discern Texas's goal - to make it too risky for an abortion clinic to operate in the State, thereby preventing women throughout Texas from exercising their constitutional rights, while simultaneously thwarting judicial review."

At the briefing, Mr Garland said a "scheme to nullify the Constitution of the United States is one that all Americans, whatever their politics or party, should fear".

He said the greater risk was that other states might follow Texas' example with regards to any such rights, warning that his department would then bring similar lawsuits against them.

Democratic President Joe Biden has been under increasing pressure to act after the law went into effect on 1 September.

Last week, Mr Biden vowed a "whole-of-government" response. He called the Supreme Court's decision to not block the law "an unprecedented assault" on women's rights.

Earlier this week, the justice department announced it would protect Texas clinics that performed abortions.

SB8 bans abortions following the detection of what anti-abortion activists call a foetal heartbeat.

The American College of Obstetricians and Gynaecologists has said the term is misleading and what is being detected at such an early stage of pregnancy is a portion of foetal tissue "that will become the heart as the embryo develops".

The law also gives individuals the right to sue anyone who provides or facilitates access to an abortion past the six-week point. It does not allow the women who get the procedure to be sued.

People who successfully sue under the law will be awarded at least $10,000 (£7,200), in addition to any legal fees incurred.

Critics, like the American Civil Liberties Union, have said that this leaves the responsibility for enforcing it on individuals, rather than local or state officials, and could give rise to abortion "bounty hunters".

Texas' Republican Governor Greg Abbott has defended the law, vowing that his state will "always defend the right to life".

Officials in several other US states have said they are considering similar laws.

In Florida, state Senate leader Wilton Simpson told reporters that the ban has "encouraged" local politicians, who are "already working" on a similar bill. South Dakota's governor Kristi Noem said she has directed her office's "unborn child advocate" to make sure the state has anti-abortion laws "on the books".