It particularly pointed a finger at Russia for supplying weapons to the Syrian regime, the BBC reported Saturday.
SNC leader Moaz al-Khatib said three weeks ago he would meet with representatives of Syrian President Bashar Assad. The change of heart means al-Khatib will not attend next month's meeting of the Friends of Syria in Rome and that the SNC will turn down invitations for talks in Washington and Moscow.
In a statement, the SNC said, "The international silence on the crimes committed every day against our people amounts to participating in two years of killings, The Russian leadership especially bears moral and political responsibility for supplying the regime with weapons."
Scud missiles supplied by Russia were "systematically" destroying Aleppo and "hundreds of civilians" have been killed, the statement added.