A Downing Street spokesperson said UK Prime Minister David Cameron -- who also talked with his Canadian counterpart Stephen Harper -- spoke Saturday to Obama.
"They reiterated that significant use of chemical weapons would merit a serious response from the international community and both have tasked officials to examine all the options," the spokesperson said.
The White House issued a statement on the same conversation, saying the two leaders agreed to "consult closely regarding this incident, as well as possible responses by the international community to the use of chemical weapons."
If the claims that Syria used chemical weapons prove true, a speedy response will be needed to prevent another such attack, U.S. Defense Secretary Chuck Hagel said.
Hagel's comments Friday came after a senior Defense Department official told CNN that military planners have updated Syrian target lists.
And it was disclosed that a fourth U.S. ship armed with cruise missiles has arrived in the eastern Mediterranean Sea.
Hagel addressed the issue aboard a military plane headed to Malaysia.
"We will determine at some point here very shortly what did happen," he said, according to a transcript posted on the Defense Department's website.
"If, in fact, this was a deliberate use and attack by the Syrian government on its own people using chemical weapons, there may be another attack coming," Hagel said. "A very quick assessment of what happened and whatever appropriate response should be made."
Hagel said the American military provided Obama "with options for all contingencies, and that requires positioning our forces, positioning our assets to be able to carry out different options, whatever options the president might choose."
He did not specify what those options might include.
Hagel predicted other nations would lend their support if the investigation finds that the Syrian government used chemical weapons against its people.
"This is an international community issue; it violates every standard of international behavior," he said. "That said, the United States has never given up its own sovereign right to protect its own interests."
The president has said he does not anticipate using ground forces in Syria. Other military options could include airstrikes by fighter jets or cruise missiles.
The Navy destroyer USS Ramage has arrived in the region, a defense official said late Friday. It was intended to replace the USS Mahan, but the Mahan will remain temporarily along with the USS Gravelly and USS Barry. All four are equipped with cruise missiles.
The president has authorized a limited amount of military hardware for the rebels in addition to logistical and humanitarian assistance.
A senior Defense Department official told CNN that options for direct military action include targeting al-Assad's capability to deliver chemical weapons.
Target lists could include government buildings and military installations, the official said, but the military must have flexible plans to target forces and equipment which "continue to move."
Sen. John McCain, R-Arizona, an advocate for a more forceful U.S. response to the Syrian conflict, has suggested that American air power could take out runways and planes used by al-Assad's forces that he said are "dominating the battlefields and the towns and the cities."
McCain also has advocated giving rebels anti-aircraft and anti-missile weapons to establish a no fly zone. But administration officials have cautioned that some Syrian rebel factions have ties to al Qaeda terrorists.
Joint Chiefs Chairman Gen. Martin Dempsey said this week in a letter to a member of Congress that arming rebels requires "choosing one among many sides."
"It is my belief that the side we choose must be ready to promote their interests and ours when the balance shifts in their favor," Dempsey wrote. "Today, they are not."
Also Saturday, a top U.N. official arrived in Damascus to press the government to cooperate in the investigation into its alleged use of chemical weapons.
Angela Kane, the United Nations high representative for disarmament affairs, has been instructed by U.N. Secretary General Ban Ki-moon to push the government to cooperate with the U.N. team already on the ground.
U.N. inspectors want to reach the site of the alleged chemical weapons attack quickly in order to gather evidence while it is still fresh. Opposition leaders say the reported attack killed more than 1,300 people in a Damascus suburb.