The UN on Tuesday condemned the execution by the government of Iraq's autonomous Kurdish region of three people convicted of murder and kidnapping, in the first use of the death penalty in the region in seven years.

Farhad Jaafar Mahmood and his two wives, Khuncha Hassan Ismaeil and Berivan Haider Karim, were hanged in the early hours of August 12, after being convicted of kidnapping and murdering two girls.

"We are dismayed to learn of the executions," Rupert Colville, a spokesman for the UN rights office, told reporters in Geneva.

The three-province autonomous government, which is still financially dependent on Iraq, put in place an informal moratorium on the use of the death penalty in 2008.

"We are deeply disappointed by this new development," Colville said, urging Kurdish officials "to recommit to and formalise its unofficial moratorium on the use of the death penalty."

A spokesman for the Kurdish Higher Judicial Council, Omid Mohsen, said regional President Massud Barzani had approved the decision.

"It is an exceptional case," Mohsen told AFP, without discussing further details of the crime or the convicts.

Colville pointed out that until now, the situation in Kurdistan had stood "in stark contrast to the situation in the rest of Iraq".

More than 600 people have been executed in Iraq since the country reinstated the death penalty in 2004. Half of those executions came in 2012 and 2013, with an additional 62 in 2014.