The Syrian government, the United Nations and the Organization of Islamic Cooperation team will begin a joint humanitarian assessment of besieged towns in Syria this weekend, the U.N. aid chief said yesterday.

The mission, after a year of bloody turmoil in Syria, will be led by the government and "observe first-hand the conditions in various towns and cities," Valerie Amos said in a statement.

The announcement came as U.N. Secretary-General Ban Ki-moon's office said Syrian President Bashar al-Assad's crackdown on a revolt had killed "well over 8,000" people.

The government blames foreign-backed militants for the deaths of more than 2,500 members of the security forces.

Amos repeated calls for the government to allow unhindered access for humanitarian organizations to enable them to help "in a neutral and impartial manner."

The joint team will go to Homs, Hama, Tartous, Latakia, Aleppo, rural Damascus, Deraa and other towns. Idlib, most recently the focus of a Syrian government offensive against rebels, was not listed in the statement.

Several diplomats told Reuters Amos had wanted the team to visit Idlib but the Syrian government did not include the city on the final list.

Official Syrian media said earlier on Thursday that government forces had cleared "armed terrorists" from the northwestern city.

Amos traveled to Syria last week and visited Homs, including the heavily shelled neighborhood of Baba Amr, which she described as devastated after a month-long siege.

On Thursday, she said it was "increasingly vital that humanitarian organizations have unhindered access to identify urgent needs and provide emergency care and basic supplies. There is no time to waste."

Ban's statement urged the government and opposition to cooperate with U.N.-Arab League envoy Kofi Annan to end the violence and called the status quo "indefensible."

It said Ban "stands in solidarity with the people of Syria and their legitimate aspirations to dignity, freedom and justice. He calls for all violence to end, and for a resolution of the crisis through peaceful means."

The Secretary-General's special advisers on the prevention of genocide, Francis Deng, and on the responsibility to protect, Edward Luck, said a lack of unified international condemnation had encouraged the Syrian government to continue its action.

"The lack of timely and decisive action by the international community has left the Syrian population to fend for itself," they said in a statement. "There is strong and growing evidence that crimes against humanity are being committed in Syria."

"To prevent further rounds of violence, which could have devastating effects for the country and the region, the government must stop its attacks on the people of Syria now," Deng and Luck said.

Annan is to brief the U.N. Security Council via video link on Friday.

Council diplomats say his assessment of the crisis will be crucial to a bid by the United States and its European allies to pass a resolution that would also ensure humanitarian aid workers have access to besieged towns across the country. Russia and China have twice vetoed resolutions condemning Syria.

Talks between the five permanent Security Council members and Morocco on a draft resolution have stalled, but are expected to pick up again after Annan's briefing, U.N. diplomats said.