An apparent gas attack in Damascus is thought to be the most significant use of chemical weapons since the gassing of Kurds 25 years ago. (AFP)
"We are expecting an attack at any moment. We are ready to retaliate at any moment," said the security official, who wished to remain anonymous, on Saturday.
US President Barack Obama on Friday gave his clearest indication yet that an attack was imminent after his intelligence experts concluded Syria's regime had unleashed poison gas on civilians.
UN experts investigating a poison gas attack in Syria left on Saturday, paving the way for the United States to lead military strikes to punish Syria's President Bashar al-Assad.
Obama said the United States, which has five cruise-missile equipped destroyers in the region, is planning a "limited, narrow" military action to punish Assad for an attack that Washington said killed 1 429 people.
"We cannot accept a world where women and children and innocent civilians are gassed on a terrible scale," Obama said on Friday after Washington unveiled an intelligence assessment concluding Assad's forces were to blame for the attack.
After laying out the case in a televised speech, US Secretary of State John Kerry spoke on Friday to the foreign ministers of European and Gulf allies, as well as the head of the Arab League, a senior state department official said.
The team of UN experts drove up to Beirut International Airport on Saturday after crossing the land border into Lebanon by road earlier in the day. No Western intervention had been expected as long as they were still on the ground in Syria.
Putin's response
Meanwhile, Russia's President Vladimir Putin said on Saturday it would be "utter nonsense" for the Syrian government to use chemical weapons when it was winning its war with rebels, and urged Obama not to attack Syrian forces.
Putin told journalists that if Obama had evidence Assad's forces had the chemical weapons and launched the attack, Washington should present it to the UN weapons inspectors and the Security Council.
"I am convinced that it [the chemical attack] is nothing more than a provocation by those who want to drag other countries into the Syrian conflict, and who want to win the support of powerful members of the international arena, especially the United States," Putin said.
The Russian president said Obama, as a Nobel Peace Prize laureate, should remember the impact any US attack would have on Syrian civilians.
World powers should discuss the Syrian crisis at a meeting of the leaders of the Group of 20 developed and developing nations in St Petersburg next week, he added. "This [G20 summit] is a good platform to discuss the problem. Why not use it?" Putin said. – AFP; Reuters