Obama defends Syria plan

US President Barack Obama remains firm in his belief that Assad is behind the killings.

FILE: Barack Obama answers questions at a news conference. Picture: AFP

JOHANNESBURG - Failing to respond to chemical weapon attacks in Syria will only increase the risk of further strikes against civilians in the country, United States (US) President Barack Obama said on Wednesday.

The US is preparing for potential military intervention in the Middle-East nation in response to August's alleged nerve gas attack by forces loyal to Syrian President Bashar al-Assad.

According to US officials, more than 1,400 men, women and children died in the attack outside the Syrian capital Damascus.

Obama remains firm in his belief that Assad is behind the killings.

Speaking alongside Swedish Prime Minister Fredrik Reinfeldt on Wednesday afternoon, Obama said the rules around these weapons are clear.

"The world set a red line when governments representing 98 percent of the world's population said the use of chemical weapons is abhorrent and passed a treaty forbidding their use, even when countries are engaged in war."

Obama says the US did not make the rules itself.

He says the international community's credibility is on the line.

"We give lip service to the notion that these international norms are important. When those videos first broke and you saw images of over 400 children subjected to [nerve] gas, everybody expressed outrage."

Meanwhile, Russian president Vladimir Putin says the US Congress has no right to approve the use of force against Syria without a decision by the United Nations Security Council.

He warned any military action without UN approval will amount to "an act of aggression".