BEIRUT — The Syrian government today dismissed U.S. charges that it used chemical weapons as “full of lies,” accusing President Barack Obama of resorting to fabrications to justify his decision to arm Syrian rebels.

The U.S. decision to begin arming the rebels, though details have not been completed, marks a deepening of U.S. involvement in Syria’s two-year civil war. It comes as President Bashar Assad’s forces have been scoring victories, driving rebels out of a key town near the Lebanese border and launching offensives in the center and north, targeting Aleppo, the nation’s largest city.

A statement issued today by the Syrian Foreign Ministry said, “The White House has issued a statement full of lies about the use of chemical weapons in Syria based on fabricated information. The United States is using cheap tactics to justify President Barack Obama’s decision to arm the Syrian opposition,\.”

U.S. officials said the administration could provide the rebel fighters with a range of weapons, including small arms, ammunition, assault rifles and a variety of anti-tank weaponry such as shoulder-fired rocket-propelled grenades and other missiles.

In addition to the increased military aid, the U.S. also announced Thursday it had conclusive evidence that Assad’s regime has used chemical weapons, including the nerve agent sarin, on a small scale against opposition forces. The White House said multiple chemical attacks last year killed up to 150 people.

Obama has said the use of chemical weapons cross a “red line” triggering greater U.S involvement in the crisis.