DAMASCUS: The US and its allies Tuesday 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 on Monday 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.
"It was a very productive day," UN spokesman Farhan Haq told reporters, adding that the team, led by Swedish expert Aake Sellstroem, was "already gathering valuable evidence".
UN Secretary General Ban Ki-moon said despite the "very dangerous circumstances" the investigators "interviewed witnesses, survivors and doctors" and "collected some samples".
The UN team was in a buffer zone between government and opposition-held areas when it came under attack.
Ban said the United Nations had made a "strong complaint" to the Syrian government and opposition forces, which traded blame for the sniper fire just as they did the chemical attacks.
The United States accused government forces of resuming their shelling of the attack site soon after the UN team departed in a bid to destroy evidence.
President Vladimir Putin of Russia -- which provides Syria's regime with diplomatic cover by blocking UN Security Council action -- was unimpressed by the mounting evidence of an atrocity.
Putin on Monday told British Prime Minister David Cameron there was no proof Damascus had used chemical weapons, according to Cameron's office.
Cameron cut short his holiday on Monday to return to London to plan a response. Britain, along with France, has been in the forefront of demands for tougher action against Assad.
Senior military officers from Western and Muslim countries began gathering in Jordan Monday to discuss the regional impact of the war in Syria, Jordanian officials said.
US army chief General Martin Dempsey was to take part, along with chiefs of staff from Saudi Arabia, Qatar, Turkey, Britain, France, Germany, Italy and Canada, state media cited an official as saying.
A senior Jordanian official, however, told AFP that "Jordanian territories will not be used as launchpad for any military action against Damascus".
Cyprus also said it did not believe a British air base on the island would play a "substantial role" in possible attacks.
A senior Israeli delegation meanwhile visited the White House for high-level talks on the Syrian crisis and the showdown over Iran's controversial nuclear programme.
The Syrian opposition says more than 1,300 people died when toxic gases were unleashed on two neighbourhoods on the outskirts of Damascus on August 21.
Syria approved the UN inspection on Sunday, but US officials said it was too little, too late, arguing that persistent shelling had "corrupted" the site.
With China and Moscow expected to boycott any UN resolution backing a military strike, British Foreign Secretary William Hague said the West could act even without full Security Council backing.
A spokesman for the prime minister also said Britain's armed forces were drawing up contingency plans for action in Syria.
There is also precedent for Obama to act militarily without US congressional backing, despite a law technically requiring it.
The alleged gas attacks are only the latest atrocity in a conflict that has claimed more than 100,000 lives since March 2011.
Assad, in an interview with a Russian newspaper published Monday, denied accusations his government was behind the attacks, calling the charges an "insult to common sense".