The US and its allies today edged closer to launching strikes against Syria, accused of deadly chemical weapons attacks that UN arms experts are investigating for a second day.
Russia, the Damascus regime's most powerful ally, warned however that any use of force would have "catastrophic consequences" while calling on the United States to show "prudence" and adhere to international law.
It also voiced regret that Washington had scrapped a planned meeting with it this week on the Syria crisis.
The Washington Post cited senior administration officials as saying President Barack Obama was weighing limited military strikes on targets in Syria.
Such action would probably last no more than two days and involve missiles or long-range bomber planes, striking military targets not directly related to Syria's chemical weapons arsenal, the newspaper said.
The report also said Washington and its allies would likely wait until the departure of a team of UN inspectors in Syria before launching strikes.
The group was originally due to leave Syria on Sunday, but their stay could be extended as they investigate allegations of chemical weapons use in the brutal 29-month conflict.
US Secretary of State John Kerry accused President Bashar al-Assad's regime of a cover-up, but said Washington would provide more evidence of who was behind the attacks.
"Let me be clear. The indiscriminate slaughter of civilians, the killing of women and children and innocent bystanders by chemical weapons is a moral obscenity," said Kerry.
"We have additional information about this attack, and that information is being compiled and reviewed together with our partners, and we will provide that information in the days ahead.
"Make no mistake. President Obama believes there must be accountability for those who would use the world's most heinous weapons against the world's most vulnerable people."
Kerry spoke after UN inspectors met survivors of the attacks, which the independent medical agency Doctors Without Borders has said left at least 355 people dead from "neurotoxic symptoms".
The UN convoy had come under sniper fire yesterday as it tried to approach the Damascus suburb where one of the attacks was reported, but the team managed to visit victims receiving treatment in two nearby hospitals.
