The United Nations estimates at least 5,000 people were killed by security forces since an uprising against Syrian President Bashar Assad began in March. The regime contends its dealing with an insurgency ostensibly supported by foreign elements.
Last year, Syrian officials agreed to pull military forces from the streets under the terms of an Arab League proposal. Arab monitors are in Syria to verify the regime's compliance, though critics accuse Damascus of hiding violence from the group.
Burhan Ghalioun, leader of the opposition Syrian National Council, said the Arab League was giving the regime political cover to continue its assault on anti-government protesters.
"If they could convey just a tiny shred of what's happening, that's more than enough to condemn the regime, to prove they have been telling lies since the beginning," he told the BBC.
He said Arab monitors either needed to prove their independence or end their mission. Western allies, he added, should consider a limited no-fly zone over parts of the country.
Washington said this week it was out of patience with efforts in Syria and it was time for the U.N. Security Council to take action.
"We only agreed to the Arab League monitoring mission because it was going to expose the regime," added Ghalioun. "We were never relying on it to stop the killing."