Kofi Annan is quitting his role as the United Nation's peace envoy for Syria, citing his frustration with the lack of unity in the U.N Security Council.

"At a time when we need -- when the Syrian people desperately need action -- there continues to be finger-pointing and name-calling in the Security Council," Annan said.

The former U.N. secretary-general said he could not continue without the New York-based, 15-nation Security Council fully backing him.

"Things fell apart in New York," he said. "The increasing militarization on the ground [in Syria] and the clear lack of unity in the Security Council have fundamentally changed the circumstances for the effective exercise of my role."

Annan's abrupt resignation caught the United Nations and world leaders by surprise.

The White House blamed Russia's and China's repeated refusal to back resolutions against the Assad regime for the resignation.

The special envoy will step down at the end of the month after trying unsuccessfully to end Syria's 17-month old conflict.