WASHINGTON, Jan. 13 (CNA) - The United States government executed convicted murderer Lisa Montgomery, the only woman on federal death row, early on Wednesday (Jan 13), after the US Supreme Court cleared the last hurdle for her execution by overturning a stay, according to a reporter serving as a media witness.

Montgomery's execution marked the first time the US government had implemented the death sentence for a female prisoner since 1953.

Challenges were fought across multiple federal courts on whether to allow the execution of Montgomery, 52, who had initially been scheduled to be put to death by lethal injections of pentobarbital, a powerful barbiturate, on Tuesday in the Justice Department's execution chamber at its prison in Terre Haute, Indiana.

Kelley Henry, Montgomery's lawyer, in scathing remarks, called the pending execution "vicious, unlawful and (an) unnecessary exercise of authoritarian power".

"No one can credibly dispute Mrs Montgomery's long-standing debilitating mental disease - diagnosed and treated for the first time by the Bureau of Prisons' own doctors," Henry said in a statement.

Montgomery was convicted of killing 23-year-old Bobbie Jo Stinnett in the north-west Missouri town of Skidmore in December 2004. She used a rope to strangle Stinnett, who was eight months pregnant, and then cut the baby girl from the womb with a kitchen knife, authorities said.

Montgomery took the child with her and attempted to pass the girl off as her own, prosecutors said.

Some of Stinnett's relatives had travelled to witness Montgomery's execution, the Justice Department said.

Montgomery's lawyers asked for Trump's clemency last week, saying she committed her crime after a childhood in which she was abused and repeatedly raped by her stepfather and his friends, and so should instead face life in prison.

It is one of three executions the US Department of Justice had scheduled for the final full week of President Donald Trump's administration. Two other executions scheduled for Thursday and Friday have been delayed, for now at least, by a federal judge in Washington, to allow the inmates to recover from COVID-19.

Federal executions had been on pause for 17 years, and only three men had been executed by the federal government since 1963, until the practice was resumed last year under Trump, whose outspoken support for capital punishment long predates his entry into politics.

Earlier on Wednesday, the Supreme Court cleared the way for the Justice Department to carry out Montgomery's execution.

The court lifted an injunction that had been put in place by the 8th US Circuit Court of Appeals that had temporarily halted Montgomery’s execution. It came hours after the Supreme Court also lifted a separate injunction by the US Circuit Court of Appeals for the District of Columbia.

The last woman executed by the federal government was Bonnie Brown Heady on Dec 18, 1953, for the kidnapping and murder of a six-year-old boy in Missouri.

The last woman executed by a state was Kelly Gissendaner, 47, on Sep 30, 2015, in Georgia. She was convicted of murder in the 1997 slaying of her husband after she conspired with her lover, who stabbed Douglas Gissendaner to death.