Japan should consider diversifying its foreign reserves from the dollar and buying International Monetary Fund bonds, according to the top finance official in the Democratic Party of Japan.

"In the medium to long term, we need to do what we can to avoid the risk of currency losses or economic turbulence that could result if the dollar were to swing," Masaharu Nakagawa, the DPJ's shadow finance minister, said in an interview Thursday. "Many countries are starting to diversify their reserves."

The DPJ overtook Prime Minister Taro Aso's Liberal Democratic Party on Sunday to become the biggest party in the Tokyo Metropolitan Assembly.