TANKS ADVANCE ON SITE

The team of UN chemical weapons inspectors arrived in Syria three days before Wednesday's attack to investigate previous reports of chemical weapons use.

Since Wednesday, the 20-strong team has been waiting in a hotel in Damascus a few miles from the site of what appears to have been the world's worst chemical weapons attack since Saddam Hussein's forces gassed thousands of Iraqi Kurds in 1988.

Their movements must be agreed with the Syrian government, and their inability to reach the site of attacks just a short drive away was symbolic of the failure of global diplomacy to have any real impact during two and a half years of war.

State television showed footage of tanks moving on Sunday into what it said was the eastern Damascus suburb of Jobar, one of the districts where the mass poisoning occurred.

Opposition activists in Damascus said the army was using surface-to-surface missiles and artillery in the area.

"The fact is that much of the evidence could have been destroyed by that artillery bombardment," said Britain's Hague.

Obama met his top military and national security advisers on Saturday to debate options. US naval forces have been repositioned in the Mediterranean to give Obama the option of an armed strike.

Assad's two main allies spoke out in his defense. Iran, echoing Obama's own language, said Washington should not cross a "red line" by attacking Syria. Russia welcomed the decision to allow the UN investigation and said it would be a "tragic mistake" to jump to conclusions over who was to blame.

It is not clear how much impact the UN investigation would have on decision-making by Western countries.

In past incidents, the United States, Britain and France obtained what they said was their own proof that Assad used small amounts of chemical arms. But if the UN team obtains independent evidence, it could be easier to build a diplomatic case for intervention.

BODIES

Throughout a war that has killed more than 100,000 people, the United States and its allies have yet to take direct action, despite saying long ago that Assad must be removed from power.

In June, after concluding that Assad's forces had used a small amount of nerve gas, Obama authorized sending US weapons to Syrian rebels. Those shipments were delayed due to fears that radical Sunni Islamist groups in the opposition could gain further ground in Syria and become a threat to the West.

However, Obama is reluctant for the United States to be drawn into another war in the Muslim world after pulling US forces out of Iraq and preparing to withdraw from Afghanistan.

Senator Jack Reed from Obama's Democratic Party said any response had to have international military support and Washington could not get into a "general military operation".

About 60 percent of Americans surveyed in a Reuters/Ipsos poll published on Saturday opposed US intervention. Nine percent thought Obama should act.

The Syrian opposition says between 500 and well over 1,000 civilians were killed by gas in munitions fired by pro-government forces. The medical charity Medecins Sans Frontieres said three hospitals near Damascus had reported 355 deaths in the space of three hours out of about 3,600 admissions with neurotoxic symptoms.

The head of the al Qaeda-linked Nusra Front rebel group has pledged to target communities from Assad's Alawite sect with rockets in revenge.

"For every chemical rocket that had fallen on our people in Damascus, one of their villages will, by the will of God, pay for it," Abu Mohammad al-Golani said in a recording on YouTube.