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Samantha Power, America's new ambassador to the United Nations, skipped a major Security Council meeting Wednesday on the alleged chemical weapons attack in Syria, a move that drew sharp criticism considering her past comments denouncing the council's inaction on the violence.

The strike early Wednesday could stand as the deadliest such incident since the country's civil war began, with reports of hundreds dying. The U.N. Security Council called an emergency meeting Wednesday afternoon to debate the allegations, but ended up issuing a statement that fell far short of what the U.S. and its allies wanted.

Yet Power herself did not attend the emergency meeting. She was instead represented by career diplomat Ambassador Rosemary DiCarlo.

A U.S. mission official told Fox News that Power was on a pre-arranged personal trip that left her unable to get back to the U.N. in time, but maintained that she was focusing closely on the Syria attack.

"Ambassador Power has secure communications and has been in constant contact with her staff and the White House," the official said. "She is monitoring events, participated in the National Security Council meeting on Egypt convened by the president, and is providing instructions to her staff."

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    One of the Obama administration's most vocal critics of its U.N. operation, though, blasted Power for her absence.

    "Samantha Power has been on the job exactly 19 days. In that time, she's already traveled from New York to Los Angeles to deliver a speech. Her absence from the UN on Wednesday sends a terrible message at a time when U.S. credibility in the region is suffering," Richard Grenell, a former U.N. spokesman under the George W. Bush administration, wrote in an online column.

    Grenell also told Fox News that her absence at this meeting could "scar her career."

    The White House is digging deeper into the alleged attacks, confirming that President Obama ordered the U.S. intelligence community to probe the latest attacks and gather evidence to find out what happened.

    Separately, State Department spokeswoman Jen Psaki said the U.S. at this point is "unable to conclusively determine" that chemical weapons were used.

    Psaki also declined, twice, to say where Power was during Wednesday's meeting.

    Asked by Fox News if she was on vacation, Psaki said: "I don't have any more details for you."

    Asked again, Psaki said: "She had a previously scheduled trip. I don't think I need to go into more detail from here."

    Other principal ambassadors from western nations were also missing at Wednesday's meeting. But Power's absence was notable considering her impassioned condemnation of the Security Council before she was sworn in.

    During her confirmation hearing, she testified that the failure of the Security Council to act on Syria is a "disgrace that history will judge harshly."

    She tackled Syria again during an online Twitter town hall she hosted last week. She said helping Syrian refugees is a priority. "Need peace so Syrians can lives safe at home," she tweeted.

    She tweeted about the latest allegations on Wednesday, writing: "Yesterday:  Reports devastating: 100s dead in streets, including kids killed by chem weapons. UN must get there fast & if true, perps must face justice."

    In her absence, the Security Council stopped short of calling for a probe on the latest alleged chemical attack amid pushback from the Russians and the Chinese, despite the fact a U.N. team is already in the country to investigate prior attacks.

    The White House spoke out on the slaughter in a written statement on Wednesday. Spokesman Josh Earnest said the U.S. is "deeply concerned" by the reports, and urged the U.N. to investigate.

    But the Obama administration continues to face criticism from lawmakers that it has remained "on the sidelines" despite warning a year ago that using chemical weapons would constitute crossing a "red line."

    "Because these threats have not been backed up by any real consequences, they have rung hollow," Sen. John McCain, R-Ariz., said in a statement. "As a result, the killing goes on, Assad remains in power, and his use of chemical weapons against Syrian civilians apparently continues. It is long past time for the United States and our friends and allies to respond to Assad's continuing mass atrocities in Syria with decisive actions, including limited military strikes to degrade Assad's air power and ballistic missile capabilities."

    Fox News' Ed Henry, James Rosen and Jonathan Wachtel contributed to this report.