A North Dakota governor has signed the most restrictive abortion law in the United States.

Jack Dalrymple, a Republican governor, signed a bill on Tuesday that banned the procedure in most cases once a foetal heartbeat could be detected, this can happen as early as six weeks into a pregnancy.

Supporters of abortion rights said that they would challenge the measure in court.

The law is an attempt to close the rural state's only abortion clinic.

North Dakota politicians moved last week to outlaw abortion in the state by passing a resolution defining life as starting at conception.

The measure essentially outlaws abortion in the state and is likely to come before voters in November 2014.

Dalrymple signed into law another measure on Tuesday that made the state the first to ban abortions based on genetic defects such as foetal syndrome.

Law 'unconstitutional'

Red River Women's Clinic director Tammi foetal called the new legislation extreme and unconstitutional.

Nancy Northup, the president and chief executive of the Centre for Reproductive Rights said that it planned to file a legal challenge to the six-week ban before it took effect on August 1.

"North Dakota has set a new standard for extreme hostility toward the rights and health of women, the US Constitution, and 40 years of Supreme Court precedent," Northup said in a written statement.

North Dakota is the latest state to pass measures to restrict abortions.

Arkansas passed a ban this month on most abortions after 12 weeks of pregnancy that could take effect in August if it survived expected legal challenges.

The law prohibits most abortions when a foetal heartbeat can be detected using an abdominal ultrasound.

A foetal heartbeat can generally be detected earlier using a vaginal ultrasound, but Arkansas politicians balked at requiring women to have the more invasive imaging technique.

North Dakota's legislation did not specify how a foetal heartbeat would be detected.

Doctors performing an abortion after a heartbeat is detected may face a criminal charge punishable by up to five years in prison and a $5,000 fine. Women having an abortion would not face charges.

Source: Agencies