Support for the death penalty in the United States has declined to its lowest level since 1972, according to a Gallup poll released on Tuesday.

Just 60 per cent of Americans now favour capital punishment for convicted murderers, down from a peak of 80 per cent in the mid-1990s the polling group said.

"The current era of lower support may be tied to death-penalty moratoriums in several states beginning around 2000 after several death-row inmates were later proven innocent of the crimes of which they were convicted," Gallup said.

Since 2006 six states have repealed death-penalty laws outright, including Maryland this year, Gallup said.

According to the poll, 81 per cent of Republicans, 47 per cent of Democrats and 60 per cent of independents continue to support the death penalty.

The largest decrease was found among Democrats, 75 per cent of whom supported the death penalty in 1994.

Gallup has been measuring Americans' attitudes towards capital punishment since 1936. Just 57 per cent were in favour of the death penalty in November 1972.

Support for the death penalty increased from 1976 and reached a peak in 1994, when Americans named crime as the biggest problem plaguing the nation, the report said.

Reuters