By Michelle Nichols

UNITED NATIONS (Reuters) - The United States accused Russia of grandstanding on Saturday by calling a U.N. Security Council meeting over U.S.-led coalition air strikes in Syria, as Russia said the attacks killed dozens of Syrian soldiers and could endanger a truce deal between Moscow and Washington.

The 15-member council met for an hour on Saturday evening after Russia and a war monitoring group said coalition jets bombed a Syrian army position near Deir al-Zor airport.

U.S. Ambassador to the United Nations, Samantha Power, said Washington was investigating the air strikes and "if we determine that we did indeed strike Syrian military personnel that was not our intention and we of course regret the loss of life."

She said Russia's decision to call a council meeting was "cynical and hypocritical" as Moscow had never expressed such outrage at the killing of civilians by Syrian government forces during more than five years of conflict.

"Russia really needs to stop the cheap point scoring and the grandstanding and the stunts and focus on what matters, which is implementation of something we negotiated in good faith with them," Power told reporters.

The deal reached last Saturday aims to put Syria's peace process back on track. It included a fragile nationwide truce, improved humanitarian aid access and joint military targeting of banned Islamist groups.

When asked if Saturday's air strikes spelled the end of the deal, Russian U.N. Ambassador Vitaly Churkin said: "This is a very big question mark."

"I would be very interested to see how Washington is going to react. If what Ambassador Power has done today is any indication of their possible reaction then we are in serious trouble," Churkin told reporters.

Churkin said it was a crucial time in the efforts to bring peace to Syria and the fight against terrorism. He said the United States could have waited until Moscow and Washington were to start joint military cooperation in two days instead of carrying out a "reckless" operation.

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"Who is in charge in Washington? Is it the White House or the Pentagon? Because we have heard statements from the Pentagon which simply fly in the face of what we have heard from President Obama and Secretary Kerry," he said.

Both parties to the Syrian conflict have accused each other of being responsible for aid deliveries being stuck far from Aleppo.

"All the permissions the Syrian government was supposed to give have been given for humanitarian supplies to reach people in need in various parts of Syria and that the humanitarian convoy to eastern Aleppo is supposed to leave tomorrow morning," Churkin said.

(Reporting by Michelle Nichols; Editing by Paul Simao)