There are growing calls for British Prime Minister David Cameron to consider a second vote on military action in Syria - IF more evidence against President Assad emerges.

In the US, President Barack Obama has launched an intense lobbying effort to sway skeptical lawmakers weighing whether to support a military strike against Syria.

Harlan Ullman is a US Naval Commander, political author & commentator and a senior advisor at the Atlantic Council in Washington - he spoke to Newstalk's Breakfast:

The strategy came after Secretary of State John Kerry revealed yesterday that Washington had proof Damascus used sarin gas in a deadly attack on August 21:

Secretary Kerry used Sunday political shows on US networks to suggest that the case for military intervention is growing. 

In Britain, pressure is mounting for a second vote on whether to support a strike against the Assad regime, though Mr. Cameron ruled out the use of British force following the defeat of his proposal in the Commons last week.

Assad lashes out

The rhetoric between Washington and the Syrian regime has grown increasingly hostile in recent days.

Mr Assad told state TV his country is capable of confronting any attack.

"The American threats of launching an attack against Syria will not discourage Syria away from its principles ... or its fight against terrorism supported by some regional and Western countries, first and foremost the United States of America," he said.

Arab League foreign ministers have urged the United Nations and the international community to take "deterrent" action, while blaming the regime for the alleged chemical weapons assault.

According to US estimates, up to 1,429 people, including at least 426 children, were killed in the alleged chemical attack in Damascus last month.

As the diplomatic wrangling continues, British MPs have called for answers from the Government over a chemicals trade deal with Syria signed months after the bloodshed started.

The Department for Business issued licences for the export of sodium fluoride and potassium fluoride to the war-torn country in January last year before revoking them several months later.

The chemicals are capable of being used to make nerve gas such as sarin as well as having a variety of industrial uses.

The Government said no chemicals were exported before the licence was revoked in June 2012 following EU sanctions but MPs said they intend to raise the issue at Westminster.