Americans strongly oppose US intervention in Syria's civil war and believe Washington should stay out of the conflict even if reports that Syria's government used deadly chemicals to attack civilians are confirmed, a Reuters/Ipsos poll says.

About 60 per cent of Americans surveyed said the United States should not intervene in Syria's civil war, while just 9 per cent thought President Barack Obama should act.

More Americans would back intervention if it is established that chemical weapons have been used, but even that support has dipped in recent days - just as Syria's civil war has escalated and the images of hundreds of civilians allegedly killed by chemicals appeared on television screens and the Internet.

The Reuters/Ipsos poll, taken August 19 to 23, found that 25 per cent of Americans would support US intervention if Syrian President Bashar Al-Assad's forces used chemicals to attack civilians, while 46 per cent would oppose it. That represented a decline in backing for US action since August 13, when Reuters/Ipsos tracking polls found that 30.2 per cent of Americans supported intervention in Syria if chemicals had been used, while 41.6 percent did not.

Taken together, the polls suggest that so far, the growing crisis in Syria, and the emotionally wrenching pictures from an alleged chemical attack in a Damascus suburb this week, may actually be hardening many Americans' resolve not to get involved in another conflict in the Middle East.

The results - and Reuters/Ipsos polling on the use-of-chemicals question since early June - suggest that if Obama decides to undertake military action against Assad's regime, he will do so in the face of steady opposition from an American public wary after more than a decade of war in Iraq and Afghanistan.

Some foreign and US officials - notably Republican Senator John McCain, whom Obama defeated for the presidency in 2008 - have called Obama too hesitant in deciding whether to act in Syria. But several Americans surveyed in this week's poll, including Charles Kohls, 68, a former US military officer from Maryland, praised Obama's caution.

"The United States has become too much of the world's policeman and we have become involved in too many places that should be a United Nations realm, not ours," Kohls said in an interview. "I don't think we ought to" intervene in Syria.

Kohls said the possibility of a chemical attack did not alter his belief that the United States should stay out of Syria, or any war for that matter.

CROSSING THE 'RED LINE'

Obama has called the suspected chemical attack near Damascus on Wednesday "an event of great concern" and directed US intelligence agencies to investigate the allegations of chemical use as he weighs potential responses.

The president met with his national security advisers on Saturday but US officials said he has not decided whether to intervene.

US defense officials, meanwhile, have repositioned naval forces in the Mediterranean to give Obama the option for a missile strike on Assad's regime, which has been backed by Russia and China.

Obama has been reluctant to intervene in the Syria war, where rebel forces opposed to Assad are made up of dozens of militant factions, some not friendly to the United States.

The president warned Syria's government last year that any attempt to deploy or use chemical or biological weapons would cross a "red line."

The White House said that Assad's military appeared to cross such a threshold in June, and responded to reports of Syrian troops using chemical weapons by agreeing to offer military aid to vetted groups of Syrian rebels.

It does not appear that any US weapons have been delivered to rebels so far. As the war has escalated, Obama's administration has come under increasing pressure from various governments, including those in France and Israel, to respond more forcefully to what many have called an unfolding humanitarian and political crisis.

LIKE OBAMA, AMERICANS CAUTIOUS

However, Obama does not appear to be feeling much pressure over Syria from the American people.

In this week's Reuters/Ipsos survey of 1,448 people, just 27 per cent said they supported his decision to send arms to some Syrian rebels; 47 per cent were opposed. The poll has a margin of error of plus or minus 2.9 percentage points for each number.

About 11 per cent said Obama should do more to intervene in Syria than sending arms to the rebels, while 89 per cent said he should not help the rebels.

Obama is considering a range of options. The most popular option among Americans: not intervening in Syria at all. That option is backed by 37 per cent of Americans, according to the poll.

Less popular options include air strikes to help the rebels (supported by 12 per cent of Americans); imposing a "no-fly" zone over Syria that would ground Assad's air force (11 per cent); funding a multi-national invasion of Syria (9 per cent), and invading Syria with US troops (4 per cent).

Deborah Powell, 58, of California, said she initially opposed any involvement by the United States but now supports arming the rebels.

"I was against any involvement after watching a (television) programme that said if we give (rebels) the weapons they could turn them against us, but I think now we need to give them the weapons," Powell said.

Asked what changed her mind, she said: "What's going on over there is terrible." However, Powell praised Obama's wariness toward getting the United States involved in another war.

Some Americans believe the use of chemical weapons has changed the game in Syria, and that the United States should get involved as long as other countries did, too.

Jonathan Adams, 56, of California, said that he was "happy that we didn't get involved from the start and I'm glad Obama was cautious. But I think we have gotten past the point of where we should've been involved in some way."

He said reports of chemical weapons use "went way past the line." - Reuters