US President Barack Obama says the US has concluded that the Syrian government carried out a chemical weapons attacks near Damascus.
He said the use of chemical weapons affected US national interests and sending a "shot across the bows" could have a positive impact on Syria's war.
But in the interview with PBS, he said he had not yet made a decision about whether to intervene militarily.
His comments follow a day of behind-the-scenes wrangling at the UN.
The UK had been pushing for permanent members of the UN Security Council to adopt a resolution which would have authorised measures to protect civilians in Syria.
However, Syrian ally Russia refused to agree to the resolution and the meeting produced no end to the diplomatic stalemate which has long characterised the UN position on Syria.
The US State Department criticised "Russian intransigence" and said it could not allow diplomatic paralysis to serve as a shield for the Syrian leadership.
Critics have questioned what purpose a limited strike on Syria could serve, but Mr Obama said it would send the government of Bashar al-Assad "a pretty strong signal that it better not do it [use chemical weapons] again".
The US has yet to produce the intelligence it says shows Mr Assad's government is guilty of using chemical weapons, and UN weapons inspectors are still investigating inside Syria.
UN Secretary General Ban Ki-moon has said they need four more days to complete their investigations and has appealed for the team to be "given time to do its job".
Syria denies using chemical weapons and blames opposition fighters for the attack on 21 August, which reportedly killed hundreds of people near Damascus.
It accused the West of "inventing" excuses to launch a strike.
"Western countries, starting with the United States, are inventing fake scenarios and fictitious alibis to intervene militarily in Syria," Prime Minister Wael al-Halqi said on Syrian state television.
In a separate development, Syria's ambassador to the UN, Bashar Jaafari, asked for the inspectors to investigate what he said were three cases of the use of chemical weapons in the last week against "dozens" of government troops in Damascus suburbs.
President Obama told the Public Broadcasting Service (PBS) that the US had concluded that the Syrian government carried out the chemical weapons attack.
"There need to be international consequences, so we are consulting with our allies," the president said.
There was "a prospect that chemical weapons could be directed at us - and we want to make sure that doesn't happen".
But Mr Obama said he was still evaluating options for possible military retaliation, and had come to no final decision on what course to take.
The BBC's David Willis in Washington says this is the most unequivocal that Mr Obama has been that the Syrian government is guilty of deploying chemical weapons.
Despite that, our correspondent says, Mr Obama looked cautious and spoke in a measured way, and he was clearly concerned about getting Congress on board as well as the American public.
Opinion polls until now have shown very little interest among the US public in getting involved in the Syrian conflict.
In an open letter to the president, US House of Representatives Speaker John Boehner demanded he explain "the intended effect of military strikes".
Mr Boehner, a Republican, asked whether there would be further strikes in the event of further "humanitarian atrocities", and whether action would be escalated should Mr Assad escalate the use of chemical weapons.
He said that there had not yet been enough consultation and explanation to secure the backing of Congress and the US public for military action.
The US has said it will not take action alone - but one of its primary allies, the UK, has agreed to wait until UN inspectors report back before taking a final parliamentary vote on potential action.
Russia rejected a UK push to try to agree a resolution on Syria among permanent UN Security Council members on Wednesday, with Foreign Minister Sergei Lavrov saying the UN could not consider any draft resolution or proposed action in Syria before the UN weapons inspectors reported back.
The use of force without a sanction of the UN Security Council would be a "crude violation" of international law and "lead to the long-term destabilisation of the situation in the country and the region", Mr Lavrov has said.
The meeting of the five permanent members has now finished, but the UK, US and France are continuing talks.
The UK will want to be seen as exhausting every diplomatic avenue, says the BBC's Nick Bryant at the UN headquarters in New York.
For the UK, there needs to be a UN "moment" - despite the fact that UN action will likely be blocked by Russia or China.
But even without UN backing the US and its allies have been clear that they see the military option is still open to them, our correspondent says.
US State Department spokeswoman Marie Harf said the US could "not be held up in responding by Russia's intransigence - continued intransigence - at the United Nations".
"This is the first use of chemical warfare in the 21st Century," said UK Foreign Secretary William Hague. "It has to be unacceptable... or we will confront even bigger war crimes in the future."
More than 100,000 people are estimated to have died since the conflict erupted in Syria in March 2011, and the conflict has produced at least 1.7 million refugees.