The USS Harry S Truman has joined the USS Nimitz in the Arabian Sea. (file photo)
WASHINGTON (AP) -- President Barack Obama says the U.S. has concluded that the Syrian government carried out a large-scale chemical weapons attack against civilians last week.
Obama says the U.S. has examined evidence and doesn't believe the opposition fighting the Syrian government possessed chemical weapons or the means to deliver them.
Obama says he hasn't made a decision about how the U.S. will respond.
The White House says it's planning a possible military response while seeking support from international partners. But the U.S. has not yet presented concrete proof of Syrian government involvement in the attack.
Some lawmakers are calling for Obama to seek congressional approval for a military action.
US officials: Navy boosts carrier presence in Gulf
U.S. officials say the Navy is beefing up its presence in the Persian Gulf region, increasing the number of aircraft carriers from one to two.
The USS Harry S Truman has arrived in the Arabian Sea and was scheduled to take the place of the USS Nimitz, which was supposed to head home. The Navy has ordered the Nimitz, which is in the Indian Ocean, to stay for now.
U.S. officials describe the decision as prudent planning and say it doesn't suggest the carrier would play a role in any possible strikes in Syria. The officials were not authorized to discuss ship movements publicly and spoke on condition of anonymity.
The U.S. had kept two carriers in the region, but budget cuts in February forced officials to cut to one.
Fears of a possible U.S. strike against Syria's regime over an alleged chemical weapons attack are rippling across the region.
On Wednesday about 6,000 Syrians fled to neighboring Lebanon and Israelis scrambled for gas masks in fear of retaliation from Syria.
Meanwhile, U.N. chief Ban Ki-moon is pleading for more time for diplomacy and to allow U.N. investigators to complete their work at the site of a suspected chemical weapons attack.