The British Parliament has been recalled for a vote this week on a possible response to an alleged chemical-weapons attack against civilians in Syria.
Earlier on August 27, Britain said its armed forces were drawing up contingency plans for possible military action in response to the attack, which activists say killed hundreds.
In France, President Francois Hollande said his country was "ready to punish" those who allegedly used chemical weapons against Syrian civilians, and that France was consulting with its allies..
Hollande said in Paris on August 27 that civil war in Syria was threatening "world peace," and announced increased military assistance to Syria's opposition.
"The chemical massacre in Damascus cannot be left without a response and France is ready to punish those who took the despicable decision to gas the innocent," Hollande said.
In London, British Prime Minister David Cameron said the world should not stand idly after the use of chemical weapons in Syria.
But he added that no decision had been made yet on how to respond to the Syria crisis, and "any decision would have to be proportionate, would have to be legal, would have to be about specifically deterring the use of chemical weapons."
Parliament is expected to vote on August 29.
In Washington, White House spokesman Jay Carney, said there was no question that chemical weapons had been used against Syrian civilians "on a massive scale." Carney said that President Barack Obama continued to review options with his national security team.
However, Carney said that "the options that we are considering are not about regime change."
Earlier on August 27, Defense Secretary Chuck Hagel told the BBC that U.S. forces stood ready to act immediately should Obama order action.
Syrian Foreign Minister Walid Muallem vowed on August 27 that Syria would defend itself using "all available means" in the event of a military attack. He said any attempt by foreign powers to create a balance of powers in Syria's war would be "delusional."
"We have two options: either to surrender, or to defend ourselves with the means at our disposal. The second choice is the best: we will defend ourselves," Muallem said, according to AFP.
Speaking to the BBC, Muallem also said that Syria rejected "utterly and completely" the accusations that it used chemical weapons.
Russia warned of the "catastrophic consequences" of any use of force.
Doctors Without Borders said last week's alleged gas attack on several sites on the outskirts of Damascus left at least 355 people dead.
Syrian President Bashar al-Assad and rebels against his regime have blamed each other for using chemical weapons in the attack.
UN Team Gathering Evidence
The Syrian foreign minister said the UN mission investigating the alleged chemical attack was delayed until August 28 after rebels failed to guarantee its safety.
The United Nations said its chemical experts in Syria delayed by one day their second trip to investigate the alleged attack as a security precaution.
On August 26, UN inspectors visited one of the sites of the alleged chemical attack, collecting what was described as "valuable evidence."
The inspectors visited Maadamiyet, a suburb southwest of Damascus, despite coming under sniper fire earlier. The Syrian government and rebels blamed each other for that attack.
In Washington on August 26, U.S. Secretary of State John Kerry described the suspected poison-gas attack as a "moral obscenity." He said those who carried out the attack should be held responsible.
"There is a reason why President Obama has made clear to the Assad regime that this international norm cannot be violated without consequences," Kerry said.
"And there is a reason why no matter what you believe about Syria, all peoples and all nations who believe in the cause of our common humanity must stand up to assure that there is accountability for the use of chemical weapons so that it never happens again."
Kerry said the United States had additional information on the attacks it would make public in the coming days.
Russia says there is no proof for the allegations Assad's forces used chemical weapons.
Russian Foreign Ministry spokesman Aleksandr Lukashevich warned on August 27 against any military intervention without UN approval.
"Attempts to bypass the [UN] Security Council and once again create artificial, groundless excuses for military intervention in the region are fraught with fresh suffering for Syria and catastrophic consequences for other countries in the Middle East and North Africa," Lukashevich said.
China's official Xinhua news agency accused Western states of rushing to conclusions about who may have used chemical weapons before UN inspectors complete their investigation.
With reporting by AFP, AP, dpa, and BBC