President Barack Obama pledged on Tuesday to explore a diplomatic plan from Russia to take away Syria's chemical weapons, but voiced skepticism about it and urged Americans to support his threat to use military force if needed.

Faced with resistance in polls and Congress to the use of force against Syria, Obama said a Russian offer to pressure President Bashar al-Assad to place his government's chemical weapons under international control raised the chances of putting off the limited military strike that he is considering.

"Over the last few days, we've seen some encouraging signs," Obama said in televised speech from the White House that attempted to offer a clear case for why it is in Americans' interests to intervene in Syria's civil war.

Obama asked leaders in Congress to put off a vote on his request to authorize the use of military force to let diplomacy play out. He said US Navy ships in the eastern Mediterranean and other forces in the region are in place and ready to respond should diplomacy fail.

The Russian initiative gave Obama some breathing space since it has been far from certain whether he would win a vote in Congress on attacking Syria in response to a chemical weapons attack last month that Washington has blamed on Assad's forces.

In a speech of only 16 minutes, Obama gave perhaps the most coherent expression of his Syria policy to date following weeks of muddled messages by his administration as opposition to a US military strike mounted.

"If we fail to act, the Assad regime will see no reason to stop using chemical weapons," said Obama. "As the ban against these weapons erodes, other tyrants will have no reason to think twice about acquiring poison gas and using them."

Under the threat of US missile strikes and with roughly half of Syria controlled by rebels, the Assad government accepted the proposal from its ally Russia earlier on Tuesday.

"It's too early to tell whether this offer will succeed. And any agreement must verify that the Assad regime keeps its commitments. But this initiative has the potential to remove the threat of chemical weapons without the use of force, particularly because Russia is one of Assad's strongest allies," said Obama.

He set no deadlines for diplomacy to run its course but said the United States will work with Russia and China to put forward a resolution at the U.N. Security Council requiring Assad to give up his supplies of sarin, mustard gas and VX nerve agents. Russia and China have been reluctant to support action against Syria.

The Russian diplomatic initiative, which emerged after off-the-cuff remarks by Secretary of State John Kerry on Monday alluding to such an idea, marked a sudden reversal following weeks in which the West seemed headed toward intervening in Syria's 2-1/2-year-old civil war.

Obama now finds himself somewhat dependent on Russian President Vladimir Putin to use his influence on Syria. It is a remarkable turnaround in relations between two leaders who are wary of each other and have bickered all year, particularly over Russia's decision to give temporary asylum to former US spy agency contractor Edward Snowden.

Some influential members of Congress were deeply skeptical about whether the diplomatic effort will succeed given US mistrust of both Russia and Assad and the difficulties of verifying chemical weapons stocks during a civil war.

Republican Senators John McCain and Lindsey Graham, two hawks on Syria, said Washington should introduce a tough U.N. Security Council resolution that lays out what steps Syria would have to take to give up its chemical weapons and threaten serious consequences if the Assad government does not.

"We would expect Russia and China to support such a resolution without delay," they said.

Obama used much of his speech to lay out the case against Syria, saying there was plenty of evidence showing that the Assad government was behind the August 21 chemical weapons attack that killed 1,429 people, including more than 400 children.

He argued that Syria should face consequences for using such weapons because much of the world has adopted a ban them. If the civilized world does nothing to respond, it will only embolden US adversaries and increase the chances that US troops might one day face these weapons on the battlefield, Obama said.

In a sign of the shifting political mood in Washington toward diplomacy, a group of Republican and Democratic senators began drafting a modified resolution on the use of military force that would give the United Nations time to take control of Syria's chemical weapons.

Obama offered a moral argument for why he feels the United States has a global obligation to respond to the Syrian chemical weapons onslaught. He portrayed the August 21 attack near Damascus in graphic terms.

"The images from this massacre are sickening: men, women, children lying in rows, killed by poison gas; others foaming at the mouth, gasping for breath; a father clutching his dead children, imploring them to get up and walk," he said.

Any US military action would be limited, he said, nothing like the Iraq and Afghanistan wars that he has spent much of his presidency winding down. No American troops will be on the ground in Syria if action is taken, Obama said.

"This would be a targeted strike to achieve a clear objective, deterring the use of chemical weapons and degrading Assad's capabilities," he said.

He insisted US military action would still have an impact, pushing back against some members of Congress who argue there is no point in doing a "pinprick" strike in Syria.

"Let me make something clear: The United States military doesn't do pinpricks. Even a limited strike will send a message to Assad that no other nation can deliver," he said.

Still, the overwhelming message from Obama was that he would like to avoid taking military action, a reflection of his personal view toward diplomacy and a response to polls showing Americans are opposed.

It was unclear if Obama had changed any hearts and minds in Congress.

Republican Congressman Chris Collins of New York said Obama's speech had moved him from being undecided to "no" on possible military action.

"I had given the commander in chief the benefit of the doubt. I was hoping the commander in chief would have a compelling argument (for military force)," said Collins. "He did not. He did not even come close."-Reuters