Arab states voted on Sunday to impose economic sanctions on Syria immediately following President Bashar al-Assad's failure to halt a crackdown on an eight-month uprising against his rule.
Qatar said that if Arab nations failed to resolve the crisis, other foreign powers could intervene.
Nineteen of the Arab League's 22 members voted for sanctions that include a travel ban on senior Syrian officials, freezing Syrian government assets, halting trade dealings with the central bank and stopping Arab investment.
The decision should be executed immediately, starting today, Qatari Prime Minister and Foreign Minister Sheikh Hamad bin Jassim al-Thani told a news conference after he chaired a meeting of Arab foreign ministers in Cairo.
The Arab League has for decades avoided taking action against its members but has been spurred into action by the scale of bloodshed during Syria's crackdown against protesters and the failure by Damascus to implement an Arab peace plan.
Arabs have said they want a regional solution and do not want foreign intervention in Syria. But France became the first major power to seek international involvement last week when it called for humanitarian corridors to protect civilians.
But the Qatari minister said foreign powers could intervene if they did not consider Arabs serious in their bid to end the crisis.
All the work that we are doing is to avoid this interference, he said.
Hundreds of people, including civilians, soldiers and army deserters, have been killed in Syria this month, possibly the bloodiest since the unrest broke out in March inspired by uprisings that overthrew leaders in Tunisia, Egypt and Libya.
(Writing by Edmund Blair; Editing by Alistair Lyon and Angus MacSwan)