TOKYO - Japanese Prime Minister Taro Aso's ruling coalition may have suffered defeat Sunday in Tokyo city elections seen as a key test of his popularity ahead of a nationwide vote, Kyodo News reported.

The opposition Democratic Party of Japan looks set to become the leading party in the Tokyo metropolitan assembly, Kyodo said, based on its own projections after the polls closed at 8:00 pm (1100 GMT).

Aso's Liberal Democratic Party (LDP) and its sole coalition partner, New Komeito, are aiming to maintain their majority in the assembly.

Experts say a big defeat for Aso's party could spark calls among LDP lawmakers for his resignation so that a new leader can take the helm ahead of general elections that he must call by September.