WASHINGTON (Reuters) - Developing countries called on the International Monetary Fund to help them deal with heightened market volatility as the U.S. Federal Reserve considers when to exit from its massive bond-buying program.

"We believe more needs to be done by the Fund to support countries in warding off global tail risks and minimizing output losses," the Group of 24 developing and emerging economies said in a communiqué on Thursday.

When asked about what more the IMF could do, Fernando Aportela, the chair of the group and Mexico's vice minister of finance, said the IMF should analyze the impact of the Fed's withdrawal, or taper, on their economies. That is something the IMF said it was already open to doing.

The G-24 also asked for more resources to help countries in the Middle East and North Africa deal with the influx of Syrian refugees. Lebanon in particular has been overwhelmed by refugees from its eastern neighbour Syria, who by the end of next year could make up 37 percent of Lebanon's pre-crisis population.

The World Bank estimated Syria's conflict will cost Lebanon $7.5 billion (4.6 billion pounds) in cumulative economic losses by the end of 2014, crimping its growth and doubling unemployment.

"We have always relied on ourselves, on Lebanese money, on Lebanese efforts," said Alain Bifani, director general of Lebanon's ministry of finance, adding that Lebanon has never defaulted on its debt. "We are now in a different situation when it comes to Syrian refugees."

U.N. agencies are preparing to launch a new appeal for aid to help victims of the Syrian conflict, which began in March 2011 and shows no sign of ending. A planned international conference to end the conflict has been repeatedly postponed and is now pencilled in for mid-November.

"The situation in Syria cannot be borne by Lebanon only," Bifani said. "It is something that creates a responsibility for the whole world, and we are hoping the whole world will be there to support our country."

(Reporting by Anna Yukhananov)