The number of death penalty executions in the United States is at the lowest point in 20 years, and death sentences themselves are at a 40-year low, according to a report released Thursday by the Death Penalty Information Center.

Executions dropped 10 percent since 2013, from 39 to 35, and just three states were responsible for 80 percent of the country's executions: Texas (10), Missouri (10), and Florida (8). A total of seven states executed people in 2014, and the number of executions has been declining since peaking in 1999, when 98 people were legally killed.

The number of new death sentences also reached its lowest level since executions resumed in 1977, with a total of 72 new death sentences so far in 2014 - seven fewer than in 2013 and 77 percent less than than in 1996.

The reduction in the number of executions coincides with an October Gallup poll that found a decline in Americans' approval of the death penalty, with 63 percent of respondents saying they favored the death penalty for convicted murders, down 17 percentage points since 1994.

The center's executive director and author of the report, Richard Dieter, notes in the release that recent botched executions, false convictions exonerations, and concerns over mental health issues of those sentenced have likely contributed to delays in carrying out death sentences as well as public outcry.

"Executions are on hold in many states, partly because of the difficulties in establishing an acceptable protocol for lethal injections. Some states tried new drugs and new combinations of drugs, resulting in three badly botched executions and an urgent call from the President and other national leaders for change. Executions were halted in Ohio, Oklahoma, and Arizona following prolonged and embarrassing procedures exposing the flaws in current protocols," Dieter said.

"When almost all of the executions are in so few of the states, you have to question the relevancy of the death penalty in the country as a whole," the report said, concluding, "Even as executions continue, there is growing concern that this sporadic and isolated use of the death penalty serves no compelling purpose.