Arkansas Republican Governor Asa Hutchinson sparked intense controversy when he announced the planned executions which he said had to be brought together because of shortages of a drug used in lethal injections.

In a statement, the EU's external affairs arm said the planned April 17-27 executions would break a de-facto death penalty moratorium in effect since November 2005 in Arkansas.

"Arkansas would also become the first State in the US to conduct seven executions over an 11-day period since the resumption of the use of the death penalty in 1977 in the United States," it said.

The 28-nation EU "opposes capital punishment, which fails to act as a deterrent to crime, represents an unacceptable denial of human dignity and integrity and cannot be justified under any circumstances," it said.

It noted that 19 of the 50 US states did not impose the death penalty, and that the number of executions has fallen steadily, hitting its lowest level in 2016.

"The executions in Arkansas, if carried out as planned, would be a serious setback in this overall development," it said.

"We therefore call on the Governor of Arkansas to commute the sentences" on the seven, it said.

An eighth man due to die last week won a stay of execution and the EU statement also called for his sentence to be commuted.

Use of the death penalty has fallen in recent years partly because procuring deadly drugs that meet constitutional standards has become more difficult.