Former Prime Minister Fumio Kishida gave gift vouchers to lawmakers from his ruling Liberal Democratic Party while he was in office, party sources said Wednesday.

The revelation emerged as incumbent Prime Minister Shigeru Ishiba comes under fire for distributing gift certificates worth ¥100,000 ($674) each to rookie LDP lawmakers.

The office of another former prime minister, Yoshihide Suga, said that he too had given gifts to LDP lawmakers.

Opposition parties are poised to increase their pressure on Ishiba and the LDP as those instances signal that Japanese prime ministers have regularly distributed money and goods to LDP lawmakers.

"This has become a structurally deep-rooted problem," Yoshihiko Noda, leader of the main opposition Constitutional Democratic Party of Japan, told reporters.

While Kishida, Ishiba's immediate predecessor, was in office, LDP lawmakers were invited to meetings at the prime minister's official residence when they became parliamentary vice ministers or state ministers, during which his staff prepared paper bags containing sweets and gift certificates for them, people familiar with the matter said.

Kishida's office said that those meetings were held appropriately in accordance with laws and regulations.

Suga's office said that the gifts he gave during his tenure were within the scope of laws and regulations.

The office of another former prime minister, Taro Aso, said that he had never distributed gift vouchers.

Several LDP officials said that gift certificates were distributed while the late former Prime Minister Shinzo Abe was in office.

A mid-ranking LDP lawmaker said that when he became a parliamentary vice minister, Abe invited him to a meeting at the prime minister's official residence where he received a gift certificate worth ¥100,000.