U.N. investigators have suspended visits to suspected chemical attack sites in Damascus suburbs for one day because of security concerns.
A U.N. statement said the team had planned to inspect one of the rebel-held suburbs on Tuesday after traveling to another affected district, Moadamiyeh, the day before. That visit was marred by sniper fire on a U.N. vehicle.
The United Nations said an assessment of the sniper fire determined that the team should wait until Wednesday before conducting another inspection, in order to "improve preparedness and safety."
The Syrian government and rebels blamed each other for the sniper attack, which damaged the U.N. vehicle but caused no casualties.
Both sides also accuse each other of responsibility for the apparent use of poison gas to kill of hundreds of civilians in the Damascus suburbs last Wednesday.
Western powers have vowed to hold the government of Syrian President Bashar al-Assad accountable for the August 21 killings, raising the prospect of their first armed intervention in Syria's two-year conflict.
But Syrian Foreign Minister Walid al-Moallem said Tuesday that the government will defend itself against any attack and surprise its enemies.
He also warned that Western attacks on Syria would serve the interests of its foe, Israel, and al-Qaida militants who Damascus blames for much of the country's violence.
Israeli Prime Minister Benjamin Netanyahu warned of a "forceful" response to any attempt by the Syrian government to attack Israel.
British Prime Minister David Cameron instructed his nation's parliament to return from its summer recess on Thursday to decide on a response to the alleged Syrian government chemical assault. An official in the French president's office said Paris "will not shirk its responsibilities" to act.
U.S. officials said a decision on Washington's response could come later this week. Members of the main opposition Syrian National Coalition told Western news agencies that Western envoys briefed them on plans to strike the Assad government "within days."
Turkish Foreign Minister Ahmet Davutoglu denounced the Syrian government's alleged chemical weapon attacks near Damascus as a "crime against humanity" and said it must "not go unanswered."
Arab League diplomats concluded a meeting in Cairo by blaming the Syrian government for the August 21 killings and calling for the perpetrators to face justice.
But Italian Foreign Minister Emma Bonino said her nation, a close ally of Washington, will not take part in any military action against Syria without a U.N. Security Council mandate. The Italian military's resources have been under strain from its longtime deployment of troops in Afghanistan.
China's state news agency Xinhua also cautioned against a rush to Western military action. In a commentary published Tuesday, it said the world should remember that the 2003 U.S.-led invasion of Iraq began with U.S. allegations that Iraqi dictator Saddam Hussein had weapons of mass destruction. Those weapons were never found.
In another development, Russian news agency Interfax said a Russian government cargo plane landed in the Syrian port of Latakia on Tuesday, delivering 20 tons of humanitarian aid for Syria's war-weary people. It said the plane also will evacuate 180 people, more than 100 of them Russian, from the country.
Moscow, a key ally of the Assad government, also has warned against Western intervention in Syria. In a Twitter message posted on Tuesday, Russian Deputy Prime Minister Dmitry Rogozin accused Western powers of behaving in the Islamic world "like a monkey with a grenade."