TOKYO, JAPAN - Japan's under pressure Prime Minister Taro Aso faced fresh calls on Friday to step down, months ahead of elections that could bring an end to his party's half-century of almost unbroken rule.

Yasufumi Tanahashi, a senior member of Aso's Liberal Democratic Party (LDP), said he had asked the embattled premier to resign due to his reluctance to support a proposal aimed at ending cushy jobs for former bureaucrats.

"The prime minister is opposed to what the public feel is right," Tanahashi, a former science minister, told reporters after meeting Aso.

"We have now no choice but to take concrete action," he said, without elaborating.

Some other ruling party lawmakers have also openly suggested the party needs a new leader to take on the resurgent opposition ahead of an election that Aso must call by September.

LDP lawmaker Taku Yamamoto has voiced open dissent against Aso and said he has collected about half of the 216 names needed to file a petition for a party leadership vote.

Aso reiterated Thursday his resolve to lead his party to victory in the next elections, saying: "I must win the race."

Recent polls have shown public support for Aso has fallen back to around 20 percent, reversing a brief bounce when his main political rival was embroiled in a funding scandal that eventually forced him to step down.

Analysts say the main opposition Democratic Party of Japan (DPJ) has a good chance of defeating the LDP at the next election.

In the latest headache for Aso, his finance minister was forced Wednesday to deny claims that he had accepted illegal political donations.

Earlier this month his communications minister stepped down over a row about the privatisation of the country's postal service.

Support for Aso, who has faced criticism for his gaffes and handling of the economy, has steadily declined since he took office last September, dipping into single digits in one poll in February.