The White House says it now has conclusive evidence that Syrian troops have used chemical weapons against rebels, a move President Barack Obama has said would cross a "red line”, Voice of America reported.

Deputy National Security Adviser Ben Rhodes told reporters Thursday, June 13 that President Obama has decided to send direct military support to the rebel fighters. But he declined to say what that support would be or when it will arrive.

Rhodes said that according to intelligence, as many as 150 people have died from multiple small-scale chemical weapons attacks over the past year. He said those numbers are likely not complete.

The national security official said sarin gas is among the chemicals used by the Syrian army. He said there is no reliable corroborated reports that the rebels also have acquired or used chemical weapons.

U.S. intelligence officials have been saying for months they were confident that chemical weapons have been used by the Syrian government. But Mr. Obama had said he needed to see firm evidence before deciding his next move.