Secretary-General Ban Ki-moon blamed the Syrian government Friday for much of the "unacceptable levels of violence and abuses" occurring every day in violation of a U.N.-backed peace plan.

In a report to the U.N. Security Council obtained by the Associated Press, Ban cited the government's continuing use of heavy weapons, reports of shelling and "a stepped-up security crackdown by the authorities that has led to massive violations of human rights by government forces and pro-government militias."

Ban lamented that there has been only "small progress" on implementing the six-point plan brokered by international envoy Kofi Annan, who is scheduled to brief the Security Council on Wednesday. Ban called on the government to keep its pledge to immediately stop the violence, pull heavy weapons and troops out of populated areas, allow humanitarian workers to help needy civilians and end human rights abuses.

Ban also called on all elements of the opposition to stop the violence and respect human rights.

He said "there have been an alarming number of explosions in population centers, including acts of terrorism," making it more imperative that all parties stop violence "to re-establish law and order," thus limiting any space for outside groups to take advantage of the situation.

The secretary-general said 271 of the 300 unarmed U.N. military observers authorized by the Security Council to help end the 15-month conflict are on the ground, and their deployment in key cities "appears to be having a calming effect."

Nonetheless, he said, "the overall level of violence in the country remains quite high" with daily incidents causing a large number of deaths and injuries, though at a lower scale than immediately before April 12 when a cease-fire was supposed to take effect.

"While the international effort is making some impact on the ground, unacceptable levels of violence and abuses are continuing in violation of ... the six-point plan," Ban said.

Although the goal of Annan's plan is to persuade the government and opposition to sit down and negotiate "no credible political process can take hold if the perception exists in a significant part of the population that its basic human rights are abused," he said.

Ban added that the situation "poses serious challenges" for the U.N. mission and the observers, who have been threatened and targeted, with their vehicles damaged and their movements restricted by crowds.

"This is a source of grave concern, and underscores the need to carefully consider the United Nations presence and next steps, taking into account the volatile and evolving security environment," Ban said.

The observers, he said, have seen "considerable physical destruction" in many locations from the conflict, with some opposition areas heavily damaged. They have also observed "that significant parts of some cities appear to be under the de facto control of opposition elements," he said.