A United Nations panel says both the Syrian government and armed rebels have committed serious human rights violations since March of this year, as violence continues despite a shaky ceasefire.

In a report released Thursday, the Independent Commission of Inquiry on Syria said the army and security forces were responsible for most of the rights violations, but the group said opposition forces share some of the blame.

The panel was established by the U.N. Human Rights Council last year to investigate the unrest that erupted when the government launched its crackdown on dissent.

It says most of the government's human rights violations were committed during search operations for defectors or for those “perceived as supportive of anti-government armed groups.”

The group says the government used lethal force against protesters in regions including Homs, Aleppo, Hama and Damascus.

It also says armed anti-government groups have killed soldiers and security forces as well as suspected pro-government supporters.

The violence has continued despite a shaky, six-week-old ceasefire brokered by international envoy Kofi Annan and the presence of U.N. monitors in Syria.

Activists say Syrian forces continued to pound the town of Rastan on Thursday, in an apparent bid to overrun militants. Rights groups say at least three people were killed in opposition-related unrest elsewhere in the country.

In another development, the opposition Syrian National Council said it had accepted the resignation of its president. Burhan Ghalioun had been facing mounting criticism of his leadership.

The political infighting had threatened to undermine international support for the Council, which is Syria's main opposition group.

Also Thursday, the state-run SANA news agency said the new 250-seat parliament convened its first session since May 7 elections. The news agency says the group will elect a Speaker and swear in assembly members.