Britain's armed forces are readying for a possible military response to an "absolutely abhorrent" suspected chemical weapons attack in Syria.

The US has given its strongest hint yet that it is ready to take action against the Assad regime following last week's apparent chemical attack in Damascus.

Prime Minister Kevin Rudd says it is "patently clear" chemical weapons were used in the strike, which opposition groups say killed more than 1,300 people.

British prime minister David Cameron, who cut short his holiday to deal with the crisis, says the attack necessitates action from the international community.

He has recalled parliament from its summer recess to debate a possible military intervention in Syria.

"We are continuing to discuss with our international partners what the right response should be, but, as part of this, we are making contingency plans for the armed forces," Mr Cameron's spokesman said.

The spokesman stressed that no decision to use force has yet been taken and that any decision to do so would be based on evidence from "a range of sources".

"This is about deterring the use of chemical weapons," the spokesman said.

Speaker agrees my request to recall Parliament on Thurs. There'll be a clear Govt motion & vote on UK response to chemical weapons attacks - David Cameron (@David_Cameron) August 27, 2013

Britain, along with the US and France, believe the Syrian regime was behind the attack.

US defence secretary Chuck Hagel says the American military is ready to launch an attack should it be given the order by president Barack Obama.

Mr Hagel backed the comments of secretary of state John Kerry, who implicated the Syrian regime in an "undeniable" chemical attack.

"We'll have more information and more intelligence here very shortly to present," Mr told the BBC.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 4 minutes 7 seconds 4 m 7 s Washington moves closer to taking action against Syria.

"I think most of our allies, most of our partners, most of the international community that we've talked (to) - and we have reached out to many - have little doubt that the most base, human, international humanitarian standard was violated in using chemical weapons against their own people."

White House spokesman Jay Carney says the US is confident the regime was behind the deadly attack, but he says Mr Obama has not yet decided what America's response will be.

"The deliberations that are taking place now and the options that are being considered by the president and his national security team are not around the question of whether or not chemical weapons were used in Syria on a significant scale, causing mass death and injury to innocent civilians, to women and children," he said.

"It is not around the question of whether the Syrian regime is responsible.

"It is around the question of what is the appropriate response."

The Arab League says the Syrian regime has "entire responsibility" for the "horrible crime carried out with internationally prohibited chemical weapons".

However, Russia's deputy prime minister Dmitry Rogozin has defended the Assad regime, accusing the West of behaving like "monkey with a grenade" in the Islamic world on Twitter.

Damascus demands evidence on chemical attack claims

The growing pressure on Damascus prompted Syria's foreign minister Walid Muallem to challenge the world to prove president Bashar al-Assad's regime was responsible for the chemical strike.

"There is no country in the world that use an ultimate destruction weapon against its own people," he said.

"If there is anyone who accuse our armed forces, have any evidence that we have used this chemical weapons, I challenge him now."

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 6 minutes 5 seconds 6 m Former chief weapons inspector Richard Butler discusses Syria's alleged use of chemical weapons.

The comments came as a United Nations team investigating the attack postponed a second day of investigations.

The team came under sniper attack on its first day of inspections but was still able to spend three hours talking samples and talking to survivors in two hospitals.

Mr Moualem says the team will head back to the sites today.

He also vowed the country will press on with its military efforts and will defend itself against any potential foreign strikes.

"We have two options: either to surrender, or to defend ourselves with the means at our disposal," he said.

"The second choice is the best: we will defend ourselves."

Assad has previously denied using chemical weapons and warned that any Western strikes against his regime would be doomed to failure.

Rudd holds talks with Obama

Mr Rudd yesterday discussed the global tensions around Syria with US president Barack Obama in a phone call.

He later used the crisis as an opportunity to question whether Tony Abbott had the temperament to deal with an international crisis such as that unfolding in Syria.

Mr Rudd said the Opposition Leader did not have a background in foreign policy and he described Mr Abbott as having an impulsive nature.

"I sometimes question, I really do question, having known Mr Abbott for a long, long time, whether he really has the temperament for that sort of thing," Mr Rudd told Seven News.

"Because you've really got to sit back, think, calmly reflect and then work through what the best decision is and temperament and judgment and experience are quite important."

Liberal frontbencher Christopher Pyne hit back at Mr Rudd for questioning Mr Abbott's temperament.

"The immediate thought I have is pot and kettle," he told Sky News.

"Quite frankly the idea that Kevin Rudd could give advice to Tony Abbott about having the right temperament to be prime minister - I mean honestly he really has lost it."

Russia warns against military intervention

Russia has warned any military intervention in Syria could have "catastrophic consequences" for the region and called on the international community to show "prudence" over the crisis.

Foreign ministry spokesman Alexander Lukashevich condemned the discussions about military action in a thinly-veiled reference to the US-led invasion of Iraq in 2003.

"Attempts to bypass the Security Council, once again to create artificial groundless excuses for a military intervention in the region, are fraught with new suffering in Syria and catastrophic consequences for other countries of the Middle East and North Africa," Mr Lukashevich said.

United Nations chemical weapons experts visit people affected by an apparent gas attack at a hospital in Damascus. ( Reuters: Abo Alhaji )

"We are calling on our American partners and all members of the world community to demonstrate prudence (and) strict observance of international law, especially the fundamental principles of the UN Charter."

Earlier, deputy foreign minister Gennady Gatilov said Moscow regretted Monday's decision by the US to postpone a meeting on the Syria crisis.

The scrapping of the meeting, which was due to take place at The Hague later in the week, is the latest sign of a new peak in tensions between Moscow and the West over the possibility of military strikes against Assad's regime.

Mr Lukashevich said that in such a climate, it was especially important to work in concert to try to organise the repeatedly-postponed peace conference bringing together the Damascus regime and the rebels.

"However, the United States' decision to postpone the meeting in The Hague is sending precisely the opposite signal to the opposition, encouraging their intransigence as they await outside intervention," he said.

ABC/AFP