ISTANBUL - The global economy faces big and crucial challenges with uncertainty and complexity in 2015, a Chinese government official said in an international financial meeting here on Sunday.

While addressing financial officials and bankers from more than 40 countries just ahead of the first Ministerial Meeting of the Turkish G20 Presidency, Chinese Deputy Finance Minister Zhu Guangyao highlighted risks for the world economy and called on joint efforts to face the challenges.

"The sluggish global growth is a real challenge faced by all members of G20," Zhu Guangyao said, referring to the downgrade of global economic growth from 3.8 percent to 3.5 percent in January by the International Monetary Fund.

Diverging monetary policies and the fall of oil price are risks causing global economic turbulence, Zhu said.

The US Federal Reserve completed the asset purchase program and is in the process of normalization of monetary policy, which is expected to raise interest rate in the middle of this year, he said.

Concerning the oil price, he said "it had already been cut down by half since last September," adding that the fall of oil price also drags down the commodity price, which "will have big impact and increase the uncertainties."

The slowdown of economic growth in Europe is another risk to the global economy as Greece casts additional uncertainties to Eurozone economy, he said.

Talking about the crisis between Russia and Ukraine, the Chinese official said that only through diplomatic channel and political consultation can solve the geo-political risk. "All concerned parties should take constructive and cooperative position to avoid worse situation."

The two-day G20 meeting held in Istanbul provides an opportunity for dialogue between senior officials and private-sector leaders in the international financial community on topics ranging from inclusive growth, job creation, private sector support for infrastructure investment and financial globalization.