ANKARA, Turkey - Turkey's high administrative court on Tuesday dealt a new blow to the main opposition party's efforts to appeal the result of a referendum that will greatly expand the powers of President Recep Tayyip Erdogan's office, rejecting a request that it overturn a controversial decision by the nation's electoral authority.

The Republican People's Party, or CHP, is contesting the April 16 referendum, citing a number of irregularities during the voting, in particular an electoral board decision to accept ballots without official stamps. International monitors also have noted irregularities and said the decision to accept the unstamped ballots as valid removed an important safeguard against fraud and was against the law.

The Council of State, the nation's highest administrative court, ruled against the CHP's request to overturn the electoral board's decision on the unstamped ballots, the state-run Anadolu Agency reported. The court said it had no jurisdiction over the electoral authority's decision.

Last week, the electoral board rejected the CHP's request to annul the referendum by a 10-1 vote. It published past rulings on the validity of unstamped ballots.

The administrative court's decision leaves the opposition party with few options. CHP officials have said they would challenge the ruling at the constitutional Court and, if necessary, at the European Court of Human Rights. Government officials have warned the CHP that the election authority's decision is final and that attempts to challenge it in the courts would be futile.

The referendum on transforming Turkey's parliamentary government system into a presidential one resulted in a narrow win for Erdogan's "yes" camp. Unofficial results, expected to be formally confirmed later this week, show the "yes" votes garnered 51.4 per cent of the vote.

The opposition fears the new system of government will concentrate too many powers in the hands of the president with few checks and balances.

The ruling Justice and Development Party, founded by Erdogan, insists the new system will usher in greater stability and prosperity.

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This version corrects the referendum result to show "yes" garnered 51.4 per cent.

News from © The Associated Press, 2017