If claims that Syria used chemical weapons several days ago are true, a speedy response will be needed to prevent another such attack, U.S. Defense Secretary Chuck Hagel said on Friday.

In addition, a senior Defense Department official told CNN that military planners have updated Syrian target lists.

The US navy is expanding its presence in the Mediterranean Sea with a fourth cruise-missile-armed warship.

The USS Mahan, a cruise-missile armed warship, which had finished its deployment in the Mediterranean and was due to head back to its home base in Norfolk, Virginia, will remain in the region, the commander of the US Sixth Fleet has decided. It will be joined by the USS Ramage, which had arrived to replace the USS Mahan.

Speaking aboard a military plane headed to Malaysia, Hagel said, “We will determine at some point here very shortly what did happen,” according to an account 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 was providing President Barack Obama “with options for all contingencies, and that requires positioning our forces [and] positioning our assets to be able to carry out whatever options the president might choose.”

He did not provide specifics on what the options were.

In a CNN interview, Obama called the alleged use of chemical weapons against civilians “a big event of grave concern,” but was very cautious as regards the possibility of using force in Syria, noting that there is still a war going on in Afghanistan.

​Meanwhile, Russian news agency RT quoted Moscow as saying the chemical attack was likely a rebel provocation.

“Materials implicating the forces of Syrian president Bashar Assad in chemical weapons use near Damascus were prepared prior to the alleged incident on August 21, the Russian foreign ministry said, according to RT.

Moscow continues to monitor closely the event surrounding the “alleged” chemical attack near Damascus, Russian Foreign Ministry spokesman, Aleksandr Lukashevich, said in a statement.

“We’re getting more new evidence that this criminal act was of a provocative nature,” he stressed. “In particular, there are reports circulating on the Internet, in particular that the materials of the incident and accusations against government troops had been posted for several hours before the so-called attack. Thus, it was a pre-planned action.”