Gulf Arab states have announced that they are withdrawing from the Arab League's observer mission in Syria.
A statement from the Gulf Co-operation Council called on the UN Security Council to take up the issue and put new pressure on the Syrian government.
It came after Damascus rejected an Arab League call for President Bashar al-Assad to hand over power to his deputy.
The UN says more than 5,000 people have died as a result of the crackdown on protests since they began last March.
Earlier, a Kuwaiti newspaper reported that the GCC did not want its monitors to be "false witnesses to crimes committed against civilians".
President Assad's supporters in the government and security forces were exploiting the observers to prevent a solution that did not suit them, al-Qabas quoted GCC officials as saying.
Saudi Arabia, the largest of the GCC's six member states, announced it would withdraw its monitors after a meeting of Arab foreign ministers on Sunday, saying Damascus had broken promises on peace initiatives.
The other GCC states are Bahrain, Kuwait, Oman, Qatar and the UAE.
The BBC's Jon Leyne Cairo says Tuesday's announcement from such influential countries is another big blow for the Arab League's mission in Syria.
The GCC's move is an illustration of how divided the Arab League is over the Syrian crisis, our correspondent says.
The monitoring mission, set up in haste in late December to observe implementation of an Arab League peace plan, seems to have a limited future, our correspondent says, even though the league extended its mandate for another month just days ago.