With less than a week to go until Sunday's election for the House of Representatives, ruling and opposition parties are working to shore up support in constituencies where the results are expected to be close.

The ruling Liberal Democratic Party is on the defensive especially in urban areas due to a slush funds scandal involving the party, leading to some executives mentioning the possibility of expanding its coalition to maintain its grip on power.

The main opposition Constitutional Democratic Party of Japan is poised to step up criticism of the ruling coalition.