TOKYO, July 10 (Aljazeera) - Voters in Japan are casting their ballots in an upper house election overshadowed by former Prime Minister Shinzo Abe’s assassination.

The election on Sunday could see the ruling Liberal Democratic Party (LDP) increase its majority.

Abe, Japan’s longest-serving prime minister who remained a dominant presence in the LDP, was gunned down on Friday while delivering a speech in support of a local candidate in the western city of Nara, a killing the political establishment condemned as an attack on democracy itself.

Prime Minister Fumio Kishida and other politicians have insisted the shock killing would not halt the democratic process.

“We must never allow violence to suppress speech during elections, which are the foundation of democracy,” he said on Saturday.

Elections for seats in the parliament’s less powerful upper house are typically seen as a referendum on the sitting government, and the latest opinion polls already pointed to a strong showing for the ruling bloc led by Kishida – an Abe protege.

As the nation mourns, both the LDP and its junior coalition partner Komeito could gain from a potential wave of sympathy votes, political analysts said.

“The ruling LDP-Komeito coalition was already on course for a solid victory,” James Brady of the Teneo consultancy said in a note. “A wave of sympathy votes now could boost the margin of victory.”

Campaigning was halted on Friday after Abe’s killing, but politicians resumed pre-election activities on Saturday.

There was an increased police presence when Kishida appeared at a campaign event in a city southwest of Tokyo and a metal detection scanner was installed at the venue – an unusual security measure in Japan.

Polls opened at 7am on Sunday (2200 GMT on Saturday) and close at 8pm (1100 GMT). Media said 15.3 percent percent of voters had cast absentee ballots in advance.