NEW YORK:The US government executed convicted murderer Lisa Montgomery, the only woman on federal death row, early on Wednesday, after the Supreme Court cleared the last hurdle for her execution by overturning a stay.

Montgomery's execution marked the first time a female prisoner has been executed since 1953 in the United States.

She was pronounced deceased at 1:31 a.m. EST (0631 GMT) on Wednesday, the Federal Bureau of Prisons said in a statement.

Challenges were fought across multiple federal courts on whether to allow execution of Montgomery, 52, who had initially been scheduled to be put to death by lethal injection 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, called the execution "vicious, unlawful, and unnecessary exercise of authoritarian power."

"No one can credibly dispute Mrs. Montgomery's longstanding 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 in 2007 in Missouri for kidnapping and strangling Bobbie Jo Stinnett, then eight months pregnant. Montgomery cut Stinnett's fetus from the womb. The child survived.

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

As the execution process began, asked by a female executioner if she had any last words, Montgomery responded in a quiet, muffled voice, "No," according to a reporter who served as a media witness.

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 resumed last year under President Donald Trump, whose outspoken support for capital punishment long predates his entry into politics.

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 U.S. Department of Justice had scheduled for the final full week of 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 condemned murderers to recover from COVID-19.

The American Civil Liberties Union and some liberal lawmakers had previously opposed the government's plans to execute Montgomery, with ACLU saying her life had been "marred by unthinkable trauma that resulted in documented brain damage and mental illness".

Montgomery's execution was the first of 2021 by the federal government and the 11th since last year.

In 2020, the U.S. government executed 10 people and it was for the first time ever that the federal government conducted more executions than all U.S. states combined, according to a database compiled by the Death Penalty Information Center.