The US will supply direct military aid to the Syrian opposition for the first time, the White House announced Friday.

President Barack Obama made the decision after his administration concluded that Syrian forces under Bashar al-Assad were using chemical weapons, including the nerve agent sarin gas, against rebels in the ongoing civil war, reported BBC citing a White House spokesperson Ben Rhodes.

On Thursday, UN High Commissioner for Human Rights Navi Pillay announced that the number of documented deaths resulting from the conflict in Syria between March 2011 and the end of April 2013 has reached 92,901.

The White House spokesperson, however, did not give details about the military aid other than saying it would be "different in scope and scale to what we have provided before".

Meanwhile, Russia said the US claims on Syria's chemical weapons' use were unconvincing.

Yury Ushakov, a senior aide to Russian President Vladimir Putin, told reporters that Washington had provided Moscow with its evidence, but "what was presented... does not look convincing to us".

Washington's "clear" statement was welcomed by NATO Secretary General Anders Fogh Rasmussen who urged Syria to let the UN "investigate all reports of chemical weapons use".

Stating that Britain agreed with Washington's assessment of Syrian regime using chemical weapons, British Foreign Secretary William Hague said an urgent response to the Syria crisis would be discussed at the G-8 meeting this week.

However, a spokesperson for UN Secretary General Ban Ki-moon told BBC that he remained against "any further militarisation" of the conflict in Syria, as he said the Syrians need peace not more weapons.