TUPELO, Mississippi (Reuters) - Mississippi executed a man on Tuesday for the 1990 murders of four of his young nieces and nephews, with the state's governor rejecting pleas for a reprieve from the mothers of the children he killed.

Henry Curtis Jackson Jr, 47, fatally stabbed two nieces and two nephews - aged 2 to 5 years - while he searched for money to steal from a safe kept in his mother's home near Greenwood, authorities said.

He was pronounced dead by lethal injection at 6:13 p.m. local time (2313 GMT) at the Mississippi State Penitentiary in Parchman, according to corrections department spokeswoman Jasmine Cole.

Regina Jackson - one of his sisters and the mother of two of his victims - said she and other family members including the mother of the other children killed had asked Mississippi's Republican Governor Phil Bryant on Monday to halt the execution.

She said the state would bring more pain to her family, not closure, by killing her brother.

"I forgave my brother. I love my brother," said Regina Jackson, who witnessed his execution along with the parents of the other young victims. "God says we got to forgive in order for Him to forgive us."

In a statement released on Tuesday, Bryant said he was touched by the requests for clemency but saw no reason to stop the death sentence from being carried out.

"There is no question that Mr. Jackson committed these heinous crimes, and there is no clear and convincing evidence that compels me to grant clemency," the governor said.

In Mississippi, the governor has the sole authority to grant clemency and can also commute death sentences to life in prison.

Jackson, called "Curtis" by his family, was the fourth person executed this year in the state and the 19th person executed in the nation.

He did not request a last meal and ate none of the standard dinner offered to him, corrections officials said. He also declined a sedative ahead of the execution.

During the attack on November 1, 1990, Regina Jackson and two other nieces were also stabbed but survived. One of them, an infant at the time, was critically injured and remained paralyzed until her death in 2009, Bryant said in his statement.

Curtis Jackson fled after the attack, prompting an extensive manhunt that ended when he turned himself in to police four days later. He admitted to the crimes but said he had no specific memory of stabbing the children, according to the Mississippi Department of Corrections.

Another convicted killer, Jan Michael Brawner, is scheduled to be put to death in Mississippi on June 12.