The six-member Gulf Cooperation Council (GCC) said on Tuesday it had decided to withdraw its monitors from an Arab League mission to Syria, following the lead of Saudi Arabia.
The League had urged Syrian President Bashar Al Assad on Sunday to step down.
Saudi Arabia had already withdrawn its monitors, and called for "all possible pressure" on Damascus.
"The GCC states have decided to respond to the decision of the kingdom of Saudi Arabia to withdraw its monitors from the Arab League delegation to Syria," the GCC said in a statement.
It said the GCC was "certain the bloodshed and killing of innocents would continue, and that the Syrian regime would not abide by the Arab League's resolutions".
GCC states on Tuesday also urged UN Security Council members to pile pressure on Syria to implement an Arab League plan to end unrest in the restive country.
The six GCC states call on "members of the UN Security Council ... to take all needed measures at the Security Council to press Syria to implement the Arab League decisions and the Arab initiative on Syria," the GCC said in a joint statement.