BRUSSELS (Reuters) - The European Union criticized Iran on Wednesday for an "alarming" increase in the use of the death penalty this year, calling on Tehran to introduce a moratorium on executions.

"According to the latest data, compiled from a number of sources, the rate of executions in Iran during the first 5 months of 2012 confirmed the country as one of the world's leading users of the death penalty," a spokesman for the EU's foreign policy chief said.

EU foreign policy chief Catherine Ashton is "deeply concerned by the alarming increase", the spokesman said.

Ashton is leading negotiations between six global powers and Iran over the Islamic Republic's nuclear program, hoping to resolve a decade-long dispute over international suspicions that Tehran seeks the means to make atom bombs. Tehran denies this.

A round of talks in Baghdad last week produced scant results but the powers -- United States, Russia, China, Germany, France and Britain -- are due to meet Iranian negotiators again in Moscow on June 18-19.

Tehran has repeatedly faced accusations of human rights abuses related to its high rate of use of the death penalty.

"It's not clear why this is happening now and might just be a coincidence. Whatever the reason may be, it's a convenient time to step up executions when the rest of the world is focusing on the nuclear talks," a Tehran-based diplomat said.

In May, Iranian media said 15 people were hanged -- 14 who faced charges of drug trafficking and a man said by Tehran to be an agent of the Israeli intelligence agency Mossad.

The EU has imposed sanctions on Iranian officials who it says play a prominent role in serious human rights violations, targeting them with travel bans and asset freezes.

Such measures are in addition to a broad range of economic sanctions the EU has introduced to press the Islamic Republic to abandon its contested nuclear activity.