A coalition of 200 aid and rights groups has called on Russia and China to support United Nations' attempts to end the violence in Syria.
Their appeal marks one year since the first protests against Syrian President Bashar al-Assad.
Syrians had survived the crackdown with "outstanding courage", the group said, but more than 8,000 had died.
The UN says it will send a humanitarian mission to Syria this weekend to assess the situation.
Its representatives will be part of a delegation led by the Syrian government.
They will also be accompanied by staff from the Organisation of Islamic Cooperation.
They will visit a number of towns including Homs, Hama and Deraa to gather information and see living conditions for themselves.
In a statement, UN humanitarian chief Valerie Amos stressed the importance of "unhindered access to identify urgent needs and provide emergency care and basic supplies".