Western powers have been mulling a military strike against Syria within?days?as punishment for alleged chemical weapons attack last week, according to media reports.

Syrian soldiers are seen at the battlefront of Jobar, near the capital of Damascus, on Aug. 24, 2013. Some Syrian soldiers on Saturday suffered suffocation after rebel militants released chemical substance around their hideouts near Damascus, the state-TV reported. [Bassem Tellawi/Xinhua]

U.S. Defence Secretary Chuck Hagel said the U.S. forces stands ready to strike Syria if President Obama gives order.

We have moved assets in place to be able to fulfil and comply with whatever option the president wishes to take," Hagel was quoted by the BBC as saying.

White House spokesman Jay Carney said on Monday "there is no doubt here that chemical weapons were used on a massive scale on August 21st outside of Damascus."

Carney believed that the Syrian regime is responsible for the use of chemical weapons, saying that "We have established with a high degree of confidence that the Syria regime has used chemical weapons already in this conflict."

"There must be a response," Carney said, adding that "what form that response will take is what the President is assessing now with his team."

But he stressed that "the options that we are considering are not about regime change. They are about responding to a clear violation of an international standard that prohibits the use of chemical weapons."

Syrian rebels said they have?been told to expect military?strike against Assad's forces soon.

"There is no precise timing... but one can speak of an imminent international intervention against the regime. It's a question of days and not weeks," AFP news agency quoted Syrian National Coalition official Ahmad Ramadan as saying.

Obama has called British Prime Minister Cameron, French President Hollande, and Australian Prime Minister Rudd and Canadian Prime Minister Harper over the past few days to discuss the potential response to the ongoing Syria crisis.

Britain's armed forces are working on contingency plans for military action as a response to "the chemical weapons attack" in Syria, media quoted Prime Minister David Cameron's spokesman as saying on Tuesday.

British Prime Minister David Cameron will continue talks with international leaders to agree a "proportionate response" that will "deter" Bashar Assad's regime from using toxic agents on the Syrian population, Downing Street said.

Cameron will chair a National Security Council meeting on Wednesday to discuss potential actions against Syria.

French President Francois Hollande on Tuesday said that his country is ready to punish the perpetrators of the suspected chemical weapons attack in Syria.

"Damascus' chemical massacre can not remain unanswered and France is ready to punish those who took the heinous decision to gas innocent civilians in Syria," Hollande stressed during an annual meeting with French ambassadors.

Hollande said he was considering all options with his European allies and Arab partners to respond to the alleged deadly chemical attack against Syrian civilians.

"Today our responsibility is ... to find the most appropriate response to these atrocities once the UN inspectors' investigation mission is completed," he added.

Syria's Foreign Minister Walid al-Moallem challenged the Western powers Tuesday to provide their evidence on the involvement of the Syrian troops in chemical?weapons use.

In an interview with a Russian newspaper on Monday, Syrian President Bashar al-Assad said Western accusations that Syrian government forces used chemical weapons are "an insult to common sense."

The latest allegations of chemical weapons use concern the Ghouta area outside Damascus. The attack, on August 21, reportedly killed more than 300 civilians including children.

Since fighting began in March 2011 between the Syrian Government and opposition groups seeking to oust President Bashar Al-Assad as many as 100,000 people have been killed, including more than 7,000 children, according to the United Nations.

In addition, almost 2 million have fled to neighbouring countries and a further 4 million have been internally displaced. At least 6.8 million Syrian require urgent humanitarian assistance, half of whom are children.