Support for the death penalty is at a four-decade low in the United States, though most Americans -- three out of five -- still favor it, a new Gallup poll out Tuesday found.

Sixty percent of Americans say they back capital punishment for convicted killers; that is the lowest figure since November 1972 when the death penalty had 57% of Americans' support, the survey found.

By 1994, eight in 10 Americans supported execution, a high from which it since has edged lower.

About 44% of respondents said the death penalty was not imposed often enough, Gallup also found in its survey of 1,028 people from October 3-6. It has a margin of error of plus or minus four points.

Of the 50 US states, 32 implement the death penalty, while 18 plus the federal capital city of Washington have abolished it.