The United States says a resolution condemning Syria's alleged poison-gas use has stalled in the UN Security Council due to Russian "intransigence."
U.S. State Department deputy spokeswoman Marie Harf said on August 28, "We see no avenue forward, given continued Russian opposition."
She spoke after Britain, China, France, Russia, and the United States discussed a British-drafted resolution that could allow military action in Syria.
Meanwhile, Western media report a British government proposal to be debated by the British Parliament on August 29 says every effort should be made to secure UN backing for military action.
Also on August 28, Russian President Vladimir Putin and Iranian President Hassan Rohani stressed during a phone conversation the need to look for ways to settle the crisis by political and diplomatic methods.
Earlier, NATO Secretary-General Anders Fogh Rasmussen said any use of chemical weapons in Syria "cannot go unanswered."
Speaking after a meeting of NATO ambassadors in Brussels on August 28, Rasmussen said information from a variety of sources pointed to President Bashar al-Assad's forces being responsible for the alleged use of chemical weapons in Syria.
British Foreign Secretary William Hague suggested Western powers would still feel bound to act even without UN support.
"We are clear that if there can't be agreement, if there isn't agreement at the United Nations, then we still have a responsibility, we and other nations still have a responsibility on chemical weapons," Hague said.
However, Russian Deputy Foreign Minister Vladimir Titov said it would be "premature" to discuss any Security Council reaction until UN inspectors investigating the attack present their report.
And UN Secretary-General Ban Ki-moon said UN inspectors needed four days to conclude their probe in Syria and their findings would then be analyzed and the result sent to the UN Security Council.
"Just days after the attacks, they have collected valuable samples and interviewed victims and witnesses," Ban said in The Hague on August 28.
"The team needs time to do its job. Here in the Peace Palace let us say -- give peace a chance. Give diplomacy a chance. Stop fighting and start talking."
On August 28, UN experts visited one of the sites of the suspected poison-gas attack near Damascus. It was the inspectors' second visit to a site of the alleged attack.
Demands For Action
Meanwhile, UN Syria envoy Lakhdar Brahimi said on August 28 in Geneva that any military action in Syria must have UN approval.
"I think international law is clear on this. International law says that military action must be taken after a decision by the Security Council," Brahimi said.
Regional powers and organizations are also contributing to the debate over Syria.
Iranian Foreign Minister Mohammad Javad Zarif warned against any strikes on Syria.
"Any kind of adventure or foreign interference in this region will definitely have consequences reaching beyond the border of [Syria] and would set the entire region ablaze," Zarif told Iranian state television.
But the Organization of Islamic Cooperation, which on August 28 blamed Damascus for the alleged gas attacks, called for "decisive action" in response.
Humanitarian organization Doctors Without Borders says that more than 300 people were killed in alleged chemical attacks on August 28 on several sites on the outskirts of Damascus.
The United States and some Western allies have blamed Assad's regime.
On August 27, U.S. Vice President Joe Biden said there was "no doubt" the Syrian government used chemical weapons and must be held accountable.
"At President Obama's direction, all of us and his national security team have been in close touch with our foreign counterparts," Biden said.
"The president believes, and I believe, that those who use chemical weapons against defenseless men, women, and children should, and must, be held accountable. "
The Syrian government has denied the claim, receiving support from Russia and China.
Russian Foreign Minister Sergei Lavrov, in a telephone call with Brahimi on August 27, warned military strikes in Syria would destabilize the country and the whole Middle East region.
Iranian Supreme Leader Ayatollah Ali Khamenei, an ally of the Assad regime, said on August 28 that intervention in Syria would be "a disaster for the region."
Meanwhile, an Al-Qaeda affiliate, the Islamic State of Iraq and the Levant, has threatened a "volcano of revenge" against Syrian government forces in retaliation for the alleged chemical attack.
The Syrian government denies it was responsible.
Syrian Ambassador to the UN Bashar Jaafar on August 28 asked the United Nations to immediately send inspectors to "investigate three instances of use of war chemicals against Syrian servicemen" in the suburbs of Damascus on August 22, 24, and 25.
With reporting by Reuters, AP, AFP, ITAR-TASS, and BBC