Updated

Turkey's electoral authority has justified its decision to validate unstamped ballots cast during the country's referendum on boosting presidential powers, citing a duty to protect citizens' right to vote.

The opposition contested the April 16 referendum which gave President Recep Tayyip Erdogan's "yes" camp a narrow victory, on grounds that the decision to count ballots without the official stamps was illegal and allowed fraud.

The High Electoral Board rejected the opposition appeal last week. In its formal justification released Thursday, it said the decision was taken to ensure that voters' ballots were not invalidated due to polling clerks' mistakes.

It said there was no evidence of fraud and rejected claims that the decision was illegal.

Turkey's main opposition party will take its appeal to the European Court of Human Rights.