Two closely watched by-election campaigns kicked off Tuesday in Hokkaido and Kyoto in what are expected to be a litmus test for how Prime Minister Shinzo Abe's ruling Liberal Democratic Party will fare in the crucial Upper House election this summer.

Some analysts say that even if the LDP loses both by-elections, which will take place April 24, Abe may dissolve the Lower House for a snap election to coincide with the Upper House poll for a double election.

Jiro Yamaguchi, a political science professor at Hosei University in Tokyo, said Abe won't want to give the opposition bloc breathing space to coordinate candidates for the Lower House, which would have more seats up for grabs than the Upper House.