WASHINGTON – Western military intervention in Syria appeared imminent on Sunday as US officials expressed confidence that the country’s embattled president, Bashar Assad, had used chemical weapons against his own people on a massive scale.Preparing military options with its allies, the US said it had “little doubt” sarin was used in the Damascus suburb of Ghouta last week, and that any UN investigation into mass chemical weapons use in Syria would, at this point, be “too late to be credible.” The comments, from a senior US administration official to The Jerusalem Post, came hours after the UN announced that the Assad regime would give its team on the ground access to the site of the alleged chemical attack.“If the Syrian government had nothing to hide and wanted to prove to the world that it had not used chemical weapons in this incident, it would have ceased its attacks on the area and granted immediate access to the UN – five days ago,” the official said.“At this juncture, the belated decision by the regime to grant access to the UN team is too late to be credible, including because the evidence available has been significantly corrupted as a result of the regime’s persistent shelling and other intentional actions over the last five days,” the official continued.Extensive evidence indicates that sarin gas was used against civilians in Ghouta on Wednesday, killing upwards of 1,000.“Based on the reported number of victims, reported symptoms of those who were killed or injured, witness accounts and other facts gathered by open sources, the US intelligence community and international partners, there is very little doubt at this point that a chemical weapon was used by the Syrian regime against civilians in this incident,” the official said.Assad officials, including the foreign minister, gave rare interviews to foreign media outlets on Saturday strongly denying claims that their government had used chemical weapons against its own people in the Damascus suburb, despite Western officials stating they have “little doubt” the attack occurred.The United Nations confirmed on Sunday that Assad’s government would grant its team access to the site, which was shelled by Assad’s forces throughout Thursday. Western government officials saw Thursday’s onslaught as an attempt to destroy evidence.A spokesman told the Post the UN was “not making any predictions” how long its investigation would take.The UN team starts work in Ghouta on Monday.The State Department has repeatedly said the US does not believe rebel forces, fighting for Assad’s ouster, have the capability to make or deliver chemical weapons.President Barack Obama has ordered the US military to prepare strike options, should he choose to move forward with an attack. The Pentagon has moved warships closer to the Syrian coast, in range of a long target list of assets of Assad’s army, including command and control centers as well as mobile units.London and Paris have been working in close concert with the White House on preparations. Britain’s Prime Minister David Cameron said on Friday that confirmation of chemical weapons use on such a mass scale would violate international standards of warfare and would require a “serious response.”Russia’s Foreign Ministry put out a statement warning the West against an attack.“We strongly urge those... trying to impose their opinion on UN experts ahead of the results of an investigation... to exercise discretion and not make tragic mistakes,” the statement read. Russia warned the US against repeating “past mistakes” in the region and going “against international law,” saying that military action would do both and would have a “devastating impact” across the Middle East.Iran on Sunday renewed its warning against Western intervention, calling US military action its own redline for direct involvement. And a Syrian official said that Western strikes would result in a “ball of fire” that would inflame the entire region.US Senators John McCain and Lindsey Graham, who have been demanding military intervention in Syria for months, renewed their call on Sunday in a joint statement.“Using stand-off weapons, without boots on the ground, and at minimal risk to our men and women in uniform, we can significantly degrade Assad’s air power and ballistic missile capabilities and help to establish and defend safe areas on the ground,” they said.Sen. Bob Corker, ranking member of the Senate Foreign Relations Committee, said on Sunday he expected Obama to order “surgical” strikes, and hopes the president will seek congressional approval for any continuation of them once the legislature returns from its August recess.The British Parliament is in recess for the summer, and could be recalled if Cameron decided to join an allied military effort. During the conflict in Libya in 2011, Parliament was convened to approve British military involvement three days after the operation began.