The US military is ready to act immediately should US President Barack Obama order action against Syria over a chemical weapons attack, US Defense Secretary Chuck Hagel said in a television interview with the BBC on Tuesday.

"We have moved assets in place to be able to fulfill and comply with whatever option the president wishes to take," Hagel said during a trip to Brunei, according to a partial transcript provided by the BBC.

Asked if the US military was ready to respond just "like that", Hagel said: "We are ready to go, like that."

Meanwhile, The Arab League on Tuesday accused the Syrian government of carrying out chemical weapons attacks in Damascus suburbs last week.

Permanent representatives condemned the "horrible crime carried out with internationally prohibited chemical weapons" and put the "entire responsibility" on President Bashar al-Assad's government at an emergency meeting in Cairo.

Syria's Foreign Minister Walid Al-Moallem said on Tuesday his country would defend itself using "all means available" in case of a US strike, denying categorically his government was behind an alleged chemical weapons attack near Damascus and challenging Washington to present proof backing up its accusations.

Moallem said at a news conference held in Damascus that his government is interested in revealing the reality behind the chemical attack that supposedly took place in the Damascus countryside. He said that the Syrian government had lived up to its part of the deal with the UN, but the rebels hindered the mission of the UN inspectors.

Regarding a possible US military attack on Syria, the top Syrian diplomat said no possible military strike would affect the government troops' advance against the rebels.

Al-Moallem spoke the day after US Secretary of State John Kerry stated there was "undeniable" evidence of a large-scale chemical attack, likely launched by the government of Assad.

Kerry used particularly tough language to refer to the alleged poison gas attack in a Damascus suburb, saying that an "international norm cannot be violated without consequences".

The remarks were the clearest justification yet for US military action in Syria. Such an attack would most likely involve sea-launched cruise missile fired at Syrian military targets.

Support for an international military response is likely to grow if it is confirmed that Assad's forces were responsible for the Aug 21 attack that activists say killed hundreds of people. Doctors Without Borders put the death toll at 355.

US President Barack Obama has yet to say how he will respond, but he appeared to be moving ahead while the UN team on the ground in Syria collected evidence from the attack.

Al-Moallem said in the news conference that US accusations that the Syrian government likely used chemical weapons were "categorically false".

"I challenge those who accuse our forces of using these weapons to come forward with the evidence," he said.

"We have the means to defend ourselves, and we will surprise everyone," he said. "We will defend ourselves using all means available. I don't want to say more than that," he added.

He declined to elaborate or say to what specific means he was referring.

He also said rebels in the capital's suburbs known as eastern Ghouta have postponed the UN team's visit by one day because gunmen could not reach agreement about guaranteeing their safety. He did not elaborate.

AP-Xinhua-AFP