WASHINGTON (Reuters) - The White House on Wednesday called on the United Nations to urgently investigate allegations of massive deadly chemical weapons use by Syrian government forces, an attack which if confirmed could increase pressure on President Barack Obama to intervene in Syria's civil war.
Syria's opposition accused President Bashar al-Assad's loyalists of gassing hundreds of people near Damascus on Wednesday with rockets that released lethal fumes over rebel-held suburbs, killing men, women and children as they slept.
While the White House said it had no independent verification of the incident and was seeking additional information, it demanded that the Syrian government allow a U.N. team already in the country "immediate and unfettered access" to the location of the alleged attack.
The United States announced on June 13 that it would send military aid to Syrian rebels, saying Assad's government had crossed a "red line" by using chemical weapons in several small-scale attacks.
But even after the announcement, Obama has stuck to a cautious approach by authorizing only limited weapons shipments, showing little appetite for deeper involvement in Syria's 2-1/2 year-old civil war.
However, with the latest allegations putting the White House on the defensive, confirmation of a large-scale gas attack could add to pressure at home and abroad for a tougher line against Assad, who has defied Western calls to step aside.
"The United States is deeply concerned by reports that hundreds of Syrian civilians have been killed in an attack by Syrian government forces, including by the use of chemical weapons, near Damascus earlier today," White House spokesman Josh Earnest said.
"We are formally requesting that the United Nations urgently investigate this new allegation. The U.N. investigative team, which is currently in Syria, is prepared to do so, and that is consistent with its purpose and mandate," he said.
Earnest said that "if the Syrian government has nothing to hide," it would facilitate the work of the U.N. inspectors. "They must have immediate access to witnesses and affected individuals, and have the ability to examine and collect physical evidence without any interference or manipulation from the Syrian government," he said.
Images, including some by freelance photographers supplied to Reuters, showed scores of bodies - some of them small children - laid on the floor of a clinic with no visible signs of injuries. Reuters was not able to verify the cause of their deaths.
The Syrian government denied it had used chemical arms, and Russia came to Assad's defense by saying the incident looked like a rebel "provocation" to discredit him.
Echoing Washington's earlier skepticism of such accusations against rebels, a U.S. official said: "We don't believe the opposition has the ability to use chemical weapons."
Unless U.N. inspectors gain access for an on-site investigation, it could take some time for U.S. officials to sift through photographs, video and intelligence to determine whether the Syrian opposition's reports are credible.
The earlier U.S. investigation of alleged Syrian chemical weapons use took months to conclude that Assad's forces had used small amounts of sarin gas in attacks during the previous year.
Obama's critics said Assad may have been emboldened by a failure to aggressively enforce the U.S. "red line" over chemical arms.
This adds to a growing perception of foreign policy troubles for Obama early in his second term. He is facing criticism for his inability to influence Egypt's generals in the country's political crisis and for failing to persuade Russia to extradite fugitive former spy agency contractor Edward Snowden.
"No consequence for Assad using chemical weapons & crossing red line - we shouldn't be surprised he's using them again," Republican U.S. Senator John McCain, a frequent critic of Obama's Syria policy, said on Twitter.
Elliott Abrams, a Middle East adviser to former President George W. Bush and supporter of stronger backing for Syrian rebels, said the Obama administration was right to get the facts first before responding.
"But if they are what they appear to be - that is hundreds of people were killed in a chemical weapons attack by the Assad regime - then I think the president's going to have to do more than issue a statement," he said. "He called this a red line, and American credibility is now very much at stake."
The White House insisted, however, it would consult international partners and allies before deciding on any response. U.S. Defense Secretary Chuck Hagel spoke about the Syrian chemical weapons reports in a call with Israeli Defense Minister Moshe Yaalon, the Pentagon said.
Additional reporting by Jeff Mason, Mark Felsenthal, Susan Heavey, Lesley Wroughton, Phil Stewart and Susan Cornwell; Editing by Vicki Allen, David Brunnstrom and Mohammad Zargham