British and American armed forces are reportedly preparing for a military engagement in Syria in response to what could be the worst chemical weapons attack since Saddam Hussein gassed thousands of Kurds 25 years ago.

The British Parliament has been recalled to debate the suspected chemical weapons attack, which the Syrian opposition says has killed over 1,300 people.

An American military response is also ready to go on President Obama’s order, according to US defence secretary Chuck Hagel.

While there had been uncertainty about whether or not chemical weapons had been used, US secretary of state John Kerry has now described the attack as “undeniable”. Australian Prime Minister Kevin Rudd similarly said it was “patently clear” that a chemical attack had occurred.

It is suspected that the chemical weapon involved was the nerve gas sarin, or something similar.

UN chemical weapons inspectors yesterday sought to collect information on the recent attack, but were forced to withdraw after being fired on by unidentified snipers.

France’s President Francois Hollande said his country would step up support for Syrian rebels and “punish those who gassed the innocent”, while an Arab League statement condemned the chemical attack.

The Syrian National Coalition says they were 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”.

Iran repeated its opposition to any US attack by saying that a military intervention will engulf the whole region. “There will definitely be perilous consequences for the region,” said Abbas Araqchi, an Iranian Foreign Ministry spokesman.

The US Navy is expanding its presence in the Mediterranean with a fourth warship armed with cruise missiles.

Assad told pro-Kremlin daily newspaper Izvestia that Syria would never be a “puppet” of the West and warned the US against attacking his country.