The United States on Saturday warned Turkey that it was alienating U.S. supporters and needed to demonstrate its commitment to partnership with the West.
The remarks, made by Philip Gordon, the Obama administration's top diplomat on European affairs, were a rare admonishment of a crucial NATO ally.
"We think Turkey remains committed to NATO, Europe and the United States, but that needs to be demonstrated," Gordon told The Associated Press in an interview.
"There are people asking questions about it in a way that is new, and that in itself is a bad thing that makes it harder for the United States to support some of the things that Turkey would like to see us support."
Gordon cited Turkey's vote against a U.S.-backed United Nations Security Council resolution on new sanctions against Iran and noted Turkish rhetoric after Israel's deadly assault on a Gaza-bound flotilla last month.
The Security Council vote came shortly after Turkey and Brazil, to Washington's dismay, had brokered a nuclear fuel-swap deal with Iran as an effort to delay or avoid new sanctions.
Turkey's ambassador to the United States, Namik Tan, expressed surprise at Gordon's comments. He said Turkey's commitment to NATO remains strong and should not be questioned.
"I think this is unfair," he said. Tan said Turkish officials have explained repeatedly to U.S. counterparts that voting against the proposed sanctions was the only credible decision after the Turkish-brokered deal with Iran.
Turkey has opposed sanctions as ineffective and damaging to its interests with an important neighbor. It has said that it hopes to maintain channels with Tehran to continue looking for a solution to the standoff over Iran's alleged nuclear arms ambitions.
"We couldn't have voted otherwise," Tan said. "We put our own credibility behind this thing."
He added that Turkish Prime Minister Recep Tayyip Erdogan was expected to discuss these issues with U.S. President Barack Obama on the sidelines of a summit of world economic powers in Toronto, Canada, on Saturday.
Some U.S. lawmakers who have supported Turkey have lashed out and warned of consequences for Ankara since the Security Council vote and the flotilla raid that left eight Turks and one Turkish-American dead. The lawmakers accused Turkey of supporting a flotilla that aimed to undermine Israel's blockade of Gaza and of cozying up to Iran.
The raid has led to chilling of ties between Turkey and Israel, countries that have long maintained a strategic alliance in the Middle East.
Gordon said Turkey's explanations of the UN episode have not been widely understood in Washington.
"There is a lot of questioning going on about Turkey's orientation and its ongoing commitment to strategic partnership with the United States," he said.
"Turkey, as a NATO ally and a strong partner of the United States not only didn't abstain but voted no, and I think that Americans haven't understood why," he added.
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