"Following a deliberative review, our intelligence community assesses that the Assad regime has used chemical weapons, including the nerve agent sarin, on a small scale against the opposition multiple times in the last year," said White House Deputy National Security Advisor Ben Rhodes in the statement.

　　"The intelligence community estimates that 100 to 150 people have died from detected chemical weapons attacks in Syria to date; however, casualty data is likely incomplete," he said.

　　Rhodes added that no "credible" evidence indicated that the Syrian rebels had used chemical weapons.

　　U.S. President Barack Obama had said evidence has pointed to the use of chemical weapons inside of Syria. He had called time and again the use of or failure to secure chemical weapons by the Syrian government a "red line" or "game changer" in his handling of the conflict in the Middle East country. But Obama had also made it clear that he needed more specific information about what had exactly happened there.

　　In the statement, Rhodes said that Washington is working with its allies to present a "credible, evidentiary" case to share with the international community.

　　"The President has said that the use of chemical weapons would change his calculus, and it has," he noted.

　　The Syrian government's actions have led to increased support by Washington to the Syrian opposition, said Rhodes, adding that the United States has other "legal, financial, diplomatic, and military responses" available.

　　"We are prepared for all contingencies, and we will make decisions on our own timeline," he said.

　　Rhodes stressed that any future U.S. action must serve its national interests and its objectives, which include achieving a negotiated political settlement, protecting the rights of all Syrians, securing unconventional and advanced conventional weapons, as well as countering terrorist activity.