The resignation of UN-Arab League joint special envoy Kofi Annan "opens gates" for a military intervention into the crisis-torn Syria, Russian Deputy Foreign Minister Gennady Gatilov said Friday.

"Annan is an honest international mediator, but someone wants to push him out of the game in order to open the gates for military actions. This is obvious," Gatilov wrote on his microblog after Annan's resignation announcement.

The deputy foreign minister also warned that Annan's decision not to extend his mandate raised many questions about the future settlement to the 17-month long Syrian crisis.

UN Secretary-General Ban Ki-moon Thursday announced the resignation of Annan.

Dialogue and diplomacy as the means to peacefully solve the Syrian crisis, as spelled out in the six-point plan proposed by Annan, has been not taken, even though it still remains the best hope for the people of Syria, Ban pointed out.

Annan, who assumed his current post about five months ago, said in Geneva on Thursday that he was disappointed over the lack of progress in the Syrian peace process and that he would step down after his current mandate expires on Aug. 31.

Vitaly Churkin, Russia's envoy to the UN, said Thursday he "regretted" the resignation of Annan and offered gratitude to his mediation efforts.

During his tenure, Annan has raised a widely accepted six-point plan, calling for the withdrawal of heavy weapons and troops from populated areas, a daily halt of fighting for the delivery of humanitarian aid and treatment of the injured, and talks between the government and opposition.