UN-Arab League joint envoy Kofi Annan on Friday appealed to participants in a Saturday meeting on Syria to "act in unison" to end the bloodshed in the Middle East country, pointing to deep involvement by external powers which is contributing to a worsening situation there.

"Many external powers are deeply involved," the former UN chief wrote in an article for The Washington Post, noting "Despite formal unity behind the six-point plan, mutual mistrust has made them work at cross-purposes."

The six-point peace plan devised by Annan has won widespread support but has failed to halt the raging violence and bloodshed in Syria. The envoy blamed the plan's non-implementation for its failure, and lamented the situation in the Arab nation as one that "could hardly be more grave."

Syrian President Bashar al-Assad said on Tuesday that his country is "in a state of a real war," calling for all polices and directives directed to win the war.

Without naming any countries, Annan said the external powers, " intentionally or otherwise," "have encouraged the government and parts of the opposition to believe that force is the only option."

"This serves no one's interest -- least of all that of the Syrian people," he asserted.

Annan announced on Wednesday that an Action Group for Syria, involving world powers and regional players, will meet on Saturday in Geneva to identify "steps and measures" to secure full implementation of the peace plan and UN Security Council resolutions 2042 and 2043, including "an immediate cessation of violence in all its forms."

"It is time for all who have influence on the parties, and all who bear responsibility for international peace and security, to act positively for peace," he wrote in his article for the American paper.

He said "The participants include those with influence on the Syrian government and its opposition. Members must commit to act in unison to end the bloodshed and implement the six-point plan, avoiding further militarization of the conflict."

"It is abundantly clear that the violence will not stop without joint, sustained pressure from those with influence, including consequences for noncompliance," he noted.

"But something more is essential. I expect all who attend Saturday's meeting to agree that a Syrian-led transition process must be achieved in accordance with clear principles and guidelines," the envoy wrote.

His new proposals also envision a Syrian government of national unity including members of the present government and the opposition. "But those whose continued presence and participation would undermine the credibility of the transition and jeopardize stability and reconciliation would be excluded," he wrote.

Russian Foreign Minister Sergei Lavrov reiterated on Thursday his country's opposition to any outside intervention in Syria or imposition of directions on Damascus.

"This also applies to Bashar al-Assad's destiny," he said at a press conference.

Washington and its allies have been pushing for the Syrian president to step aside to make way for a political transition.