Cameron had been seeking concessions for his country so that he can encourage Britons to vote for continued EU membership in a referendum expected in the coming months.
"If this does not happen, it will mean the end of the negotiations with all the possible consequences, including the worst-case scenario," European Council President Donald Tusk said.
The European Union presented a proposal to the UN Monday morning, hoping to activate a plan for handling the flood of migrants from the Middle East and Africa to Europe.
Alexis Tsipras, who led Syriza to a momentous win in the parliamentary election, was sworn in today amid fears about what his win means for the country's bailout agreements with the European Union.
A combination of political instability in Greece, possible quantitative easing in the eurozone and a stronger dollar are all pushing the common European currency lower.
Nearly 20 companies have filed antitrust complaints against Google in Europe since 2009. Under the new commissioner, the company could face more formal charges and billions of dollars in fines.
Some economists say Thursday's vote on Scotland's independence could have wide-ranging economic impacts. They fear that a breakaway from the U.K. could trigger another global financial upheaval.
U.S. and EU officials begin talks Monday on a free-trade deal that could create thousands of jobs and billions of dollars in new trade. But there are deep-seated differences that may make it difficult to reach an accord. Among the most contentious: agriculture and whether genetically modified crops grown in the U.S. will be accepted in Europe.