By Elaine Lies and Yoshifumi Takemoto

TOKYO Japanese Prime Minister Fumio Kishida is increasingly certain to call a snap election, perhaps within weeks, as domestic support surges after a G7 summit that drew a surprise visit by Ukraine's president.

While an election for parliament's more powerful lower house is not due until 2025, Kishida is keen to beef up his strength in the ruling Liberal Democratic Party (LDP) ahead of a leadership race next fall, to ensure his re-election and retain the premiership.

His party's parliamentary majority virtually guarantees its president will be prime minister.

Although Kishida said on Sunday he was not thinking of dissolving parliament now, experts feel he may not be able to resist as favourable conditions stack up.

"He's going to want to do it at the best timing, to give him good results in the LDP race, to give him a mandate," said Airo Hino, a professor of political science at Tokyo's Waseda University.

Holding an election soon would let Kishida benefit from support rates that have shot up 9 percentage points in several polls since the G7 summit began on May 19, as well as perceptions that have strengthened his image as a global leader.

Kishida, who took office in Oct 2021, saw his approval slide to just under 30% in some polls last Nov, battered by revelations of ties between the LDP and the Unification church, but numbers began to edge up with a thaw in ties with South Korea and a trip to Ukraine in March.

Hosting the summit in his home base of Hiroshima, the first city to suffer an atomic bombing in war, also played on sympathy for Ukraine and its suffering.

This received a boost from President Volodymyr Zelinskiy's unexpected appearance, as well as television images of the two leaders offering flowers at a monument to atomic bomb victims.

"For Kishida, Zelenskiy's visit has a unique significance that will help boost his support rating," said Shigenobu Tamura, a political analyst and former LDP staffer.

"In addition, Kishida chaired a summit that raised global issues and included other nations such as India and South Korea, highlighting his actions and stature in the world."

Kishida may also want to ride tailwinds from multi-decade highs in the benchmark Nikkei 225 index, fuelled by strong earnings and signs of economic revival. On Friday, it powered to its highest since 1990.

Calling an early election could mean less time for the opposition to prepare.

Few of Japan's opposition groups pose a significant threat, but the LDP has a wary eye on the growing strength of the conservative Japan Innovation Party and would like to keep it from joining hands with other parties.

Still, Kishida is expected to hold off on an announcement until his government unveils proposals to combat a falling birthrate and passes a measure to increase defence spending. The current parliamentary session ends on June 21.

But there are also significant risks.

An early election might come too soon to guarantee Kishida the LDP presidency even if the party does well, as a threat looms from rising prices, said analyst Atsuo Ito.

While the LDP has won recent elections, including a handful of by-elections this April, their victories have been far from overwhelming, he added, a point also made by other analysts.

"Prime ministers always gain popularity after summits," Ito added. "The question is whether he can keep it up."

(Additional reporting by Anton Bridge; Writing by Elaine Lies; Editing by Clarence Fernandez)