Barack Obama says his approach to military intervention in Syria is not under scrutiny - it is the credibility of the US congress and international community that is on the line.

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The US president, speaking at a press conference in Stockholm, said it is up to international government, and to congress, to decide on the US response to punish Bashar al-Assad for the use of chemical weapons in Damascus last month.

America and congress' credibility is on the line, because we give lip service to the notion that these international norms are important. Barack Obama

He said it was important to send a message that the "norm" that chemical weapons must not be used is adhered to.

"My credibility is not on the line," he said. "The international community's credibility is on the line.

"America and congress' credibility is on the line, because 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 gas, everyone expressed outrage, 'how can this happen in this modern world?'

"Well, it happened because a government chose to deploy these deadly weapons on civilian populations. And so the question is how credible is the international community when it says this is an international norm that has to be observed."

How credible?

President Obama is currently engaged in a campaign to convince the American public, and congress, to vote in favour of military intervention.

On Wednesday the Senate Foreign Relations Committee approved a resolution authorising the use of military force in Syria by 10-7, clearing the way for a vote by the full Senate expected next week.

This has not deterred both the US president and his secretary of state, John Kerry, from making a number of addresses to explain the reaons why military action is both justified and a moral responsibility.

I didn't set a red line, the world set a red line. Barack Obama

"The question is how credible is congress when it passes a treaty saying we have to forbid the use of chemical weapons," President Obama continued.

"I do think that we have to act. Because if we don't we are effectively saying that though we may condemn it and issue resolutions and so far and so on, someone who is not shamed by resolutions can continue to act with impunity.

"And those international norms begin to erode, and other despots and authoritarian regimes can start looking and saying 'that is something we can get away with''."

Red line

He also rejected suggestions that he had set a "red line" for action against Syria.

"I didn't set a red line, the world set a red line," he said. "The world set a red line when government's representing 98 per cent 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.

"Congress set a line when it ratified that treaty, congress set a red line when it indicated in a piece of legislation entitled the Syria Accountability Act that some of the horrendous things that are happening on the ground need to be accounted for."

Read more: Obama's red line on Syria - can he win the case for action?

President Obama added that he did not believe military action alone could resolve the situation in Syria.

He also said it was his right as commander-in-chief to take military action, in order to prevent US interests, but that he thought it was the right thing to do to put the issue to congress.

Speaking to a hearing of the House of Representatives foreign affairs committee on Wednesday the US Defence Secretary Chuck Hagel said that a planned military strike against Syria would not be a "pin prick", but a significant strike that would degrade President Assad's military capability.

'Shirking responsibility'

In the House of Commons on Wednesday David Cameron and Labour leader Ed Miliband clashed over last week's vote which has ruled out British military intervention in Syria.

Mr Miliband asked Mr Cameron to accept that "last week's vote was not about Britain shirking its global responsibility, it was about preventing a rush to war."

Mr Cameron responded that he accepted the Commons vote, and that he would not be bringing the issue of British military intervention back to the Commons.

But criticising Mr Miliband's decision to table an amendment to Mr Cameron's Commons motion, Mr Cameron said: "My only regret of last week vote is I didn't think it was necessary to divide the house on a vote that could have led to a vote, but he took the decision that it was."

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Both leaders appeared at times to be competing to condemn the atrocities in Syria. Mr Cameron pledged that the UK would do "everything that we can" to encourage countries to donate humanitarian funds to the crisis.

He also said that Britain needs to maintain its "strong responses" to the Syrian regime in order to push Assad's regime to talks in Geneva.

He said that "we need Assad himself to realise that it is in his own interests because he cannot win a war against his own people."