U.S. questions whether fragile Syrian truce can hold

NEW YORK (Reuters) - The United States on Monday questioned whether a fragile Syrian truce could be salvaged and put the onus on Moscow to show it is committed to ending the violence after warplanes bombed a U.N. aid convoy in Aleppo province. "This was a difficult and trying day in Syria that raises very serious questions about whether the Russians can deliver their end of the arrangement," a senior U.S. administration official told reporters. "Either way the burden is on the Russians to demonstrate quickly and in a significant way that they are committed to this process," a second administration official said, adding that it was unclear whether the bombing was by the Russians or Syrian government. (Reporting by Lesley Wroughton; Editing by Sandra Maler)