United States President Barack Obama says any military response to last week's deadly chemical attack will be limited, to avoid dragging the US into another war in the Middle East.
In a television interview, Mr Obama said he hadn't yet made a decision about military retaliation for Syria's alleged use of chemical weapons but there must be some response.
"If in fact we can take limited, tailored approaches, we send a shot across the bow saying 'stop doing this', that can have a positive impact on our national security over the long term, and may have a positive impact in the sense that chemical weapons are not used again on innocent civilians."
Mr Obama says he has no interest in having an open-ended conflict in Syria.
The State Department has criticised Russia after it earlier used a meeting of the five permanent members of the security council to block a British resolution which would have authorised measures to protect civilians from chemical attacks in Syria.
Russia says the UN must finish its investigation into the claims before discussing any resolution.
International support is growing for military intervention, in response to a poison gas attack believed to have been launched by forces loyal to President Bashar al-Assad on 21 August.
Washington and its allies in Europe and the Middle East say their minds are made up, that the Assad regime must face retribution for the use of banned weapons.
British Foreign Secretary William Hague has hinted the United Kingdom will take action over the chemical weapons attack, regardless of what the United Nations security council decides.
"We're clear that if there can't be agreement, if there isn't agreement at the United Nations, then we still have a responsibility, we and other nations, still have a responsibility on chemical weapons."
However, the government will propose to the British parliament that the UN should see a report from chemical weapons inspectors before taking action.
NATO Secretary-General Anders Fogh Rasmussen says information from a variety of sources points to President Bashar al-Assad's forces being responsible for the use of chemical weapons in Syria.
After a meeting of NATO ambassadors in Brussels, Mr Rasmussen said any use of such weapons was "unacceptable and cannot go unanswered", although he did not suggest any response.
British Foreign Secretary William Hague says if the attack is not confronted, there will be bigger war crimes in the future.
In Damascus, people are stocking up on supplies and some have left homes close to potential targets of any Western assault.
Banks have been crowded with queues of people withdrawing cash.
United Nations chemical weapons experts have made a second field trip to rebel suburbs, seeking evidence of what and who caused the attack that has brought the Syrian crisis to a head.
UN chief Ban Ki-moon has sought more time for the inspectors to complete their work. The team's mandate of 14 days expires in four days.
Syria's ambassador to the UN, Bashar Ja'afari has also called for the UN investigators to be allowed to finish their work away from any political or military pressure, saying aggression by any country would go against the United Nations Charter.
Mr Ja'afari says he wants the UN to investigate three other incidents in which Syrian government forces reportedly came under chemical assault.
The ambassador accused western powers of conspiring to derail the UN investigation that could clear the Syrian government of culpability in last week's attack.
Israel increasing defence measures
Israel has deployed extra missile defence units and called up reservists in case of retaliation by Syria or its allies if Western air strikes are launched.
Prime Minister Benjamin Netanyahu says the armed forces are ready to deal with any threat.
The BBC reports there's no sense of panic in the country but there have been queues for gas-masks and air-raid shelters in the north of the country.
Earlier, Iran's Supreme Leader Ayatollah Ali Khamenei added his voice to those warning of the dangers of military intervention in Syria, saying the whole region is like a tinderbox.