Washington said it had taken note of the "extraordinary" decision by Turkish election authorities to re-run the mayoral election in Istanbul, in a more low-key response than European allies to the annulment of a major victory by President Recep Tayyip Erdogan’s rivals.
"We, like other friends of Turkey, take note of this extraordinary decision," the State Department said in a statement issued on Wednesday, two days after the Turkish Supreme Election Council announced its decision on an appeal lodged by Mr Erdogan’s Justice and Development Party (AKP) party.
It urged Turkey to conduct the new election "in a manner that is consistent with its OSCE commitments, its status as a Nato ally, and its aspirations for membership in the European Union".
In contrast, Germany, another Nato ally, said the decision to annul the election was "not transparent, and incomprehensible to us", while the EU called for Turkey's election body to explain its reasons for holding a re-run "without delay".
Turkey's main opposition Republican People's Party (CHP) on Wednesday formally requested the annulment of President Erdogan's mandate, saying the same flaws alleged by the AKP in Istanbul's mayoral vote had occurred in last year's national elections.
The CHP also said votes for Istanbul officials and councils, submitted in the same envelopes as those for the mayoral election, should be cancelled if the mayoral vote was re-run. The AKP won a majority in the councils.
The victory by CHP candidate Ekrem Imamoglu was the first time in 25 years that the AKP or its Islamist predecessors failed to win control of Istanbul, Turkey's largest city with a budget of close to $4 billion (Dh14.7bn). Mr Erdogan launched his own political career as Istanbul mayor.
Turkey's election body on Wednesday lashed out at criticism of its decision as "unacceptable", the state-run news agency reported.
"It is unacceptable to personally target and discredit the judges because of the decision they made," the Supreme Election Council was quoted as saying by the Anadolu news agency.
The board "will continue to do its duty despite pressure, slander, insult and threats", it added.
The AKP complained of "irregularities" in voting in Istanbul during Turkey's March 31 local elections after its candidate narrowly lost to Mr Imamoglu.
The electoral body accepted the complaint and seven of its members voted this week to cancel the opposition's victory and re-run the election on June 23.