The U.N. Secretary General Ban Ki-Moon expressed his opposition over the White House's announcement to send direct military support to the rebel groups in Syria.

Opposing the plan to arm Syrian rebels, Ban Ki-Moon said that there was no certainty about the use of chemical weapons in Syria citing lack of on-ground investigation in the country.

Ban urged the Syrian government to grant access to a technical mission led by Dr. Ake Sellstrom to launch the investigation.

"The validity of any information on the alleged use of chemical weapons cannot be ensured without convincing evidence of the chain-of-custody," National Public Radio quoted the U.N. secretary general as saying.

"That is why I continue to emphasize the need for an investigation on the ground in Syria that can collect its own samples and establish the facts. The use of chemical weapons by any party would be a crime against humanity," said Ban Ki-Moon. "Given the seriousness of the allegations and the potentially grave consequences, I again urge the Syrian Government to grant Dr. Sellstrom's team the access we have long sought."

President Barack Obama Thursday warned that the U.S. government was considering arming the Syrian rebels saying that its intelligence had concluded that the Syrian forces under President Bashar al-Assad regime were using chemical weapons against the rebels who were fighting to over throw the regime.

"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 Ben Rhodes, deputy national security adviser to President Obama.

"Our intelligence community has high confidence in that assessment given multiple, independent streams of information," said Rhodes. "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."

"We have consistently said the use of chemical weapons violates international norms and crosses red lines that have existed in the international community for decades," added  Rhodes.

Rhodes didn't disclose any information about what sort of military support the administration was considering but Rhodes said that the aid would be "different in scope and scale to what we have provided before."