United Nations Secretary-General Ban Ki-moon wants to send more observers to Syria

U.N. Secretary-General Ban Ki-moon speaks during a press conference April 17, 2012, in Luxembourg.

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As a U.N.-backed cease-fire appears to be unraveling in Syria, the United Nations wants to expand the deployment of monitors there in an attempt to broker a peaceful transition under the six-point plan proposed by joint Arab League-U.N. envoy Kofi Annan.

In a letter to the Security Council, U.N. Secretary-General Ban Ki-moon proposes a supervision mission of up to 300 observers in Syria.

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"I recommend that the Council authorize such a mission, with the understanding that I will consider relevant developments on the ground, including the consolidation of the cessation of the violence, to decide on deployments," the secretary-general writes in his letter obtained by CBS News.

"The protracted crisis in Syria over the past 13 months has seen many thousands killed, injured, detained or displaced. The violence has been characterized by use of heavy weapons in civilian areas and widespread violations of human rights, while aspirations for political change in the country have not been met. I remain deeply concerned about the gravity of the situation in the country. However, without under-estimating the serious challenges ahead, an opportunity for progress may now exist, on which we need to build."

Although the secretary-general's letter says that "it appears that levels of violence dropped markedly," he adds that "the Syrian Government has yet to fully implement its initial obligations regarding the actions and deployments of its troops and heavy weapons, or to return them to barracks."

On desperately needed humanitarian aid, the letter says the U.N. and the Organization of Islamic Cooperation identified a million people in need of assistance in Syria. No substantive progress has been achieved during the last weeks of negotiations on access to those in need or in increasing the capacity of organizations on the ground.

Ban's proposal would authorize the larger group of observers for an initial period of three months.

"They would be deployed incrementally over a period of weeks, in approximately ten locations throughout Syria. It would be a nimble presence that would constantly and rapidly observe, establish and assess the facts and conditions on the ground in an objective manner, and engage all relevant parties."

Time is short. Syrian forces have continued to shell cities, opposition centers and protesters.

"We think that any U.N. mission, including any U.N. mission in Syria, needs to be able to operate with the independence, the freedom of movement, the freedom of communications, all of the traditional freedoms that are necessary for an effective and neutral U.N. presence anywhere in the world," U.S. Ambassador Susan Rice said Wednesday. "And we can't accept a set of circumstances in Syria that we wouldn't accept anywhere else or that violates 65-plus years of U.N. best practice and principle."

On Thursday, the council will be briefed by Annan's deputy Jean-Marie Guehenno and Edmond Mulet, an assistant secretary-general for peacekeeping. Annan's spokesman Ahmad Fazwi confirmed to CBS News that Annan will brief the Security Council next week.