The US says this afternoon that it has evidence that Syrian President Bashar al-Assad and his supporters have used chemical weapons against rebels fighting to oust Assad from power. The White House said that its findings will result in increased support for Syrian rebels, but it stopped short of saying that it will arm them. The next step, the White House said, is to share its findings with its allies and the United Nations.

In April, the Obama administration said that it believed Assad was using chemical weapons, including sarin gas, against rebels. But, at the time, the White House said it didn't have solid evidence of this, and it called on the UN to investigate. Since then, the US has moved forward with an investigation of its own and found over the last few weeks 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." The administration said in a statement that it has "high confidence" in its findings, which were sourced from "multiple, independent streams of information." The White House said it will provide direct support to Syrian rebels, including the Supreme Military Council. However, Ben Rhodes, a deputy national security advisor, declined in a press call to offer an inventory of what the increased support would be made up of. Yahoo's The Ticket blog has reported that US support would be geared toward "direct military purposes."

The administration said that it has evidence of the planning and execution of chemical attacks which include the time, location, and means of attack. The US has also received descriptions of "physiological symptoms that are consistent with exposure to a chemical weapons agent," notably sarin. "Each positive result indicates that an individual was exposed to sarin, but it does not tell us how or where the individuals were exposed or who was responsible for the dissemination," the White House said.

About 100 to 150 have died from chemical weapons attacks in Syria, the White House said, adding that its data is "likely incomplete" because of limited intelligence access in Syria. The US also said Syria has blocked UN investigators from launching "a comprehensive investigation as called for by the international community."

Overall, more than 90,000 people have died in the ongoing civil war in Syria, which leaves those killed by chemical weapons in the minority. But, "the use of chemical weapons violates international norms and crosses clear red lines that have existed within the international community for decades," the White House said. "We believe that the Assad regime maintains control of these weapons." The US also said it has found no reliable evidence that Syrian rebels have used chemical weapons. Both the British and French governments have also said publicly that they believe that Assad has used chemical weapons against rebels.