Secretary-General of the United Nations Ban Ki-moon announced Thursday the resignation of the?UN-League of Arab States Joint Special Envoy for the Syrian crisis, Kofi Annan.

"It is with deep regret that I have to announce the resignation of the UN-League of Arab States (AL) Joint Special Envoy for Syria, Mr. Kofi Annan," Ban said in a statement released here by his spokesperson.

Annan has informed Ban and Secretary-General of the League of Arab States Nabil Elaraby of his intention not to renew his mandate when it expires on Aug. 31, 2012, the statement said.

Ban said he wished to express his deepest gratitude to Annan for the "determined and courageous" efforts he has made as the joint special envoy.

Ban and Elaraby jointly announced the appointment of former UN chief Kofi Annan as the two organizations' joint special envoy on the Syrian crisis on Feb. 23.

The UN General Assembly adopted a resolution on Feb. 16 demanding the heads of the UN and the AL to appoint a special envoy to Syria, a country which has been troubled for months by tension and violence between anti-government protesters and the forces of President Bashar Assad.

"Kofi Annan deserves our profound admiration for the selfless way in which he has put his formidable skills and prestige to this most difficult and potentially thankless of assignments," Ban said.

The UN chief now is in consultations with Elaraby on prompt appointment of a successor who can carry on this crucial peacemaking efforts.

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

"Both the government and the opposition forces continue to demonstrate their determination to rely on ever-increasing violence. In addition, the persistent divisions within the Security Council have themselves become an obstacle to diplomacy, making the work of any mediator vastly more difficult," he said.

The UN is committed to pursue through diplomacy an end to the violence and a Syrian-led solution that meets the legitimate democratic aspirations of its people, Ban noted.

The Russian envoy to the UN Vitaly Churkin told reporters here that he "regretted" the resignation of Annan and offered gratitude to his mediation efforts.

Churkin said one of the reasons that Annan's diplomatic efforts have gone through many difficulties is that his appeal for no further militarization of the Syrian conflicts was not really heeded by some influential countries in international community.