U.S. officials said that Syria has started to move part of its chemical weapons arsenal out of storage facilities, the Wall Street Journal reported on Friday.
The country's undeclared stockpiles of sarin nerve agent, mustard gas and cyanide have long worried U.S. officials and their allies in the region, the report said.
Western nations have looked for signs amid the rebellion against President Bashar al-Assad's government of any change in the location of those weapons, believed to be the world's largest stockpile.
American officials are divided on the meaning of the moves of the arsenal. Some fear Assad may want to use the weapons against rebels or civilians, while others said perhaps he is trying to safeguard them from his opponents, the Journal reported.
U.S. State Department spokeswoman Victoria Nuland, traveling with Secretary of State Hillary Clinton in Phnom Penh, said "We repeatedly made it clear that the Syrian government has a responsibility to safeguard its stockpiles of chemical weapons."
She added that "the international community will hold accountable any Syrian officials who fail to meet that obligation."
The Syrian government denied chemical stockpiles have been moved, the Journal said.
Syria is one of eight states - along with Israel and nearby Egypt - that have not joined the 1997 Chemical Weapons Convention, which means the world's chemical weapons watchdog has no jurisdiction to intervene there.
The Assad government has in the past denied having weapons of mass destruction.