The United States military has provided Barack Obama with a range of options for launching an attack on Syria and is "ready to go" with an offensive, the US defence secretary has said.

There is now a growing belief in Washington that a US strike against Syria, possibly involving cruise missiles or long-range bombers, could take place in the next few days.

Chuck Hagel said military officials had presented the US president with "all options for all contingencies" and put resources in place to take action against Syria over its purported use of chemical weapons.

"We are prepared, we have moved assets in place to be able to fulfil and comply with whatever option the president wishes to take, if he wishes to take any of the options he's asked for," he told the BBC. "We are ready to go, like that."

The White House insisted on Tuesday that Barack Obama had still not made a decision about the use of military action, but stressed that "boots on the ground" was not an option being contemplated. "The options that we are considering are not about regime change," said White House spokesman Jay Carney.

He declined to say whether the US Congress would be required to authorise any military strike, or be recalled as has happened in Britain's parliament, but insisted the White House was consulting with leaders in the House and Senate and communicating with the chairmen of relevant congressional committees.

He said a US intelligence assessment of the chemical attack in a Damascus suburb would be published "this week".

In a sign that Obama believes he has the legal authority, independently of Congress, to launch a strike, Carney said that allowing the chemical weapons attack to go unanswered would be a "threat to the United States".

US defence officials recently said a destroyer armed with cruise missiles – one of four warships in the region – has been stationed in the eastern Mediterranean sea. Military transporters have also been spotted at Britain's Akrotiri airbase on Cyprus, less than 100 miles from the Syrian coast.

Reports from the region suggest the US is gearing up for a swift military action, possibly as soon as Thursday, in a punitive show of force against President Bashar al-Assad. Syria has denied its forces were responsible for a chemical attack in a suburb of Damascus, which is believed to have killed hundreds.

Jo Biden, the US vice-president, has become the most senior member of the Obama administration to blame the Syrian government for the attack.

Addressing a group of veterans in Houston, he said there was "no doubt who was responsible for this heinous use of chemical weapons in Syria: the Syrian regime".

He added that "those who use chemical weapons against defenceless men, women and children ... must be held accountable".

The Syrian opposition has been told to expect a strike against Syrian forces within days, according to a Reuters report of a meeting that took place on Monday. The meeting with the Syrian National Coalition took place in in Istanbul, and included senior western diplomats including Robert Ford, a top US official with responsibility for Syria.

"The opposition was told in clear terms that action to deter further use of chemical weapons by the Assad regime could come as early as in the next few days, and that they should still prepare for peace talks at Geneva," a source at the meeting told the news agency.

The chairman of the Joints Chief of Staff of the US military, General Martin Dempsey, told Congress last month that even "limited standoff strikes" against Syria would require hundreds of aircraft, ships and submarines and could cost billions of dollars.

While such action would "degrade regime capabilities" and lead to defections, Dempsey told the House Foreign Affairs committee, there was a risk of retaliatory attacks and "collateral damage impacting civilians". He also warned of "unintended consequences" of any military intervention in the complex civil war.

In Britain, there were strong signs military action could be imminent, after the prime minister David Cameron announced parliament would be recalled to vote on a motion about the country's "response to chemical weapons attacks in Syria" on Thursday.

The US would be expected to have laid out preliminary plans for any military attack, or at least expressed a clearer intent over the use of force, before any foreign government voted on on whether to support such action.

World leaders have issued a string of bellicose statements in the last 24 hours, with Iran and Russia standing alongside the Assad regime against an emerging western alliance led by the US, UK, France and Australia. Iran's foreign ministry spokesman, Abbas Araqchi, intimated that Tehran would respond, should the west strike.

US secretary of state John Kerry said on Monday that Syria had committed a "moral obscenity" and Obama was preparing a co-ordinated with response with international allies. "Make no mistake," Kerry said. "President Obama believes there must be accountability for those who would use the world's most heinous weapon against the world's most vulnerable people."

The White House, which has long been reluctant to become militarily involved in the Syrian conflict, appears to have shifted its position over the weekend, after a top intelligence officials presented evidence of the chemical attack, arguing it could only have been administered by Syrian forces.

The administration is preparing to release parts of its intelligence assessment in the coming days, as it attempts to build congressional and public support for tough action against Syria. "I think the intelligence will conclude that it wasn't the rebels who used it, and there'll probably be pretty good intelligence to show is that the Syria government was responsible," Hagel said. "But we'll wait and determine what the facts and the intelligence bear out."

He added: "In our opinion, I think the opinion of the entire world community, Syria used chemical weapons against its own people.

"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 and talked to many – have little doubt that the most base international humanitarian standard was violated in using chemical weapons against their own people."

Hagel's comments about Syria's "violation" of an international human rights standard echoed the language used by the State Department and White House. It suggests the US will attempt to mount a legal justification for any strikes, outside a UN framework, by arguing Assad's forces were responsible for a breach of humanitarian law.

Strong opposition from from Russia and China means it is highly unlikely the US will receive support for military action from the UN security council.

Although the US stresses the administration is seeking a broad coalition of partners for any action, the UN is being increasingly sidelined. Carney said on Tuesday the work of weapons inspectors now was Damascus was "redundant" because it has already been established that chemical weapons were used by Syria on a large scale.

In a further blow to the inspections process, the UN said on Tuesday that its inspectors had postponed their visit to one of the affected sites for 24 hours amid concerns for their security.

An sniper attack on the UN team on Monday led to substantial delays.

"Following yesterday's attack on the UN convoy, a comprehensive assessment determined that the visit should be postponed by one day in order to improve preparedness and safety for the team," the UN said in a statement.