TOKYO (Kyodo) -- Prime Minister Shigeru Ishiba said Thursday that his office handed out gift vouchers to rookie Liberal Democratic Party lawmakers but maintained that the practice does not pose legal problems, dealing a fresh blow to the ruling party still reeling from a slush fund scandal.

Ishiba said the gifts, delivered to the first-term lawmakers before they met for dinner at the prime minister's official residence on March 3, were intended to reward their hard work and paid out of his own pocket. A voucher gift was worth 100,000 yen ($676) per person, according to participants of the meeting.

Speaking to reporters after media reports about the incident drew immediate criticism from opposition lawmakers, Ishiba apologized for causing "worries" but ruled out stepping down over the matter.

"It wasn't a donation but was meant to be a token of appreciation for family members (of the lawmakers). I paid for the vouchers myself, and it was not against the law," Ishiba said.

"While there are no legal problems, I have to apologize for causing trouble," he added.

An aide visited the offices of lawmakers elected to the House of Representatives last October to hand out the vouchers as souvenirs before the dinner meeting got underway, but all 15 members later returned them, according to sources familiar with the matter. A person close to Ishiba said, "It was done with good intentions."

The revelation came a day after upper house lawmaker Shoji Nishida, one of the LDP's more conservative members, questioned Ishiba's leadership and called for his replacement ahead of the House of Councillors election this summer.

Besides Ishiba, the March meeting was attended by Chief Cabinet Secretary Yoshimasa Hayashi and two deputy chief Cabinet secretaries -- Keiichiro Tachibana and Kazuhiko Aoki.

One of the participants said, "I don't see any problem because I returned it. I didn't see what was inside" the paper bag delivered by Ishiba's secretary.

Japan's political funds control law bans donations from individuals to politicians to support their political activities. The distribution of vouchers could be seen as a violation of the law depending on its objective, experts said.

The Oct. 27 general election marked a turning point for the ruling coalition of the LDP and Komeito, as they lost control of the lower house amid the slush fund scandal. Since then, Ishiba has had to rely on opposition support to pass bills and budgets.

Opposition party members quickly went on the offensive against Ishiba at a sensitive time for the government, as it needs parliamentary approval for the draft budget plan for the next fiscal year starting April.

"It's out of the question from both Ishiba's side and those who accepted the gifts," Hiroshi Ogushi, executive deputy president of the main opposition Constitutional Democratic Party of Japan, told Kyodo News.

"If this is true, it means that the LDP has no regrets whatsoever over the secret money scandal," he added, in reference to revelations that some LDP members underreported portions of income from fundraising events.

A senior member of the opposition party said, "The prime minister must resign."