Ashton said Wednesday she was concerned by reports that Iraq executed a number of prisoners recently. There were more than 100 executions in Iraq last year but none in 2013 until recently.
The European Union considers the death penalty to be a violation of basic human rights and views capital punishment as no deterrent against even the harshest of crimes, Ashton said.
"Pending the abolition, I urge the Iraqi authorities to introduce a moratorium on the use of the death penalty," she said in a statement.
Iraq's post-war progress received heightened criticism as March marks the 10th anniversary of the U.S.-led invasion.
A U.S. inspector general report on the conflict said senior Iraqi officials had serious questions about whether the engagement was worth the effort.
A protest movement against Iraqi Prime Minister Nouri al-Maliki has emerged in Anbar province, once home to Iraqi insurgents. The government postponed elections scheduled for April in two provinces recently because of security concerns.