The only Native American on federal death row was executed Wednesday against the wishes of the Navajo Nation, which called the sentence an affront to its sovereignty.

Lezmond Mitchell, 38, was put to death via lethal injection in the evening at the federal prison in Terre Haute, Indiana, 19 years after he was convicted of killing a young girl and her grandmother, the prison announced.

"Justice finally has been served," said the US Justice Department spokeswoman, Kerri Kupec, in a statement.

But Mitchell's lawyers said the federal government had "added another chapter to its long history of injustices against Native American people."

Most crimes committed in the United States are tried in state courts, some of which are authorized to apply capital punishment. But federal courts can take up and try the most serious case, or crimes committed in jurisdictions outside state control, such as -- under certain conditions -- Native American reservations.

Federal courts rarely deliver capital punishment sentences and carry them out even less frequently. From 1988 until July, only three people on federal death row were executed.

Under the administration of President Donald Trump, a staunch advocate of the death sentence, executions have been stepped up, however.

Three people were executed in July. Another man on death row, Keith Nelson, 45, is scheduled for execution on Friday.

They were all convicted for the murder of children, often having committed their crimes in a particularly violent manner.

Tribal sovereignty

Mitchell was convicted of fatally stabbing a 63-year-old grandmother during a car theft in 2011 and slitting the throat and crushing the skull of her nine-year-old granddaughter. He then buried the heads and hands of the two victims.

Because the killings occurred on Navajo territory in Arizona and the victims and Mitchell were tribe members, US authorities should have obtained approval of the Navajo Nation for the death penalty, say community officials who point to a 1994 law governing Native American tribal sovereignty.

The Navajo refuse to apply capital punishment to Native Americans, and the victims' family had asked that Mitchell be sentenced to life imprisonment.

A legal challenge, concerning the sovereignty of tribal justice, failed at the last minute in the US Supreme Court.

The Republican billionaire, who is standing for re-election on November 3, has advocated expanding the use of the death penalty, in particular for those convicted of killing police officers or children and for drug traffickers.

Support for the death penalty has eroded among the general US population but remains strong among Republican voters.