The prime minister was dealt a severe blow after his ruling LDP was crushed in Sunday's Tokyo municipal election - a defeat that could foreshadow results of the imminent national polls.
The LDP and its junior coalition partner, New Komeito party, lost their majority in the Tokyo assembly while the opposition Democratic Party of Japan (DPJ) won the most seats in the vote which is considered a barometer for the national election.
"It's clear if parliament is dissolved now, the result would be the same as the Tokyo election"
Natsuo Yamaguchi, New Komeito's policy chief
The DPJ won 54 of the 127 seats at stake and together with other opposition parties wrested control from the LDP and Komeito, which garnered 38 and 23 seats respectively.
The LDP and Komeito together had previously held 70 seats to the DPJ's 34.
The LDP has now lost four straight regional elections since April to the DPJ and many in the LDP and New Komeito are opposed to holding an election so soon after their latest defeat.
"It's clear if parliament is dissolved now, the result would be the same as the Tokyo election," the New Komeito's policy chief, Natsuo Yamaguchi, told a TV Asahi programme.
The Democrats, hoping to intensify pressure on the ruling bloc, are considering submitting a no-confidence motion against Aso in the lower house as early as Monday and Yukio Hatoyama, the DPJ leader, is expected to lead his party in a boycott of parliamentary proceedings.
The LDP has been in power for all of the past 50 years except a brief period in 1993, but it has been racked by internal strife with Aso critics openly urging an early party leadership vote to replace him.
|Sunday's election defeat was the fourth straight polls setback for Aso [AFP]
According to local media, some younger LDP members who have previously expressed dissatisfaction with Aso met at a Tokyo hotel on Sunday night in the wake of the polls defeat in the capital.
But Tsuneo Watanabe, an expert on Japan's domestic and foreign policies, told Al Jazeera from Tokyo that it was very difficult for the LDP to replace Aso ahead of the polls because "people are so frustrated with the LDP for changing many party leaders".
"The LDP has been affected by the downturn and people are frustrated with the economy, but they are more frustrated with the LDP's inability to create a strong leadership," he said, noting that Yasuo Fukuda and Shinzo Abe had resigned as prime minister after serving a year or less each.
The LDP has 303 seats in the current parliament's 480-seat lower house, and its partner Komeito has 31. The DPJ has just 112.
But opinion polls by Japanese newspapers indicate the DPJ is well placed to make major gains or even rise to power in a national election, with Hatoyama likely to replace Aso.
In a nationwide survey on Friday by the Yomiuri newspaper, Japan's top-selling daily, 41 per cent of respondents said they would vote for the opposition party in the national election, compared with just 24 per cent for Aso's party.
Nearly 46 per cent of respondents said Hatoyama, 62, was fit to be prime minister, compared with 21 per cent favouring Aso.