Japan's tiny Social Democratic Party (SDP) was likely to decide on Sunday to leave the ruling coalition ahead of an election, media said, as Prime Minister Yukio Hatoyama faced calls to step down over broken campaign promises.
The departure of the SDP would be a blow to Hatoyama, already seen by voters as a weak leader, damaging his Democratic Party's chances of winning a majority in an upper house election expected in July, which it needs to pass bills smoothly.
But it would not force the Democrats out of power since they boast a massive majority in parliament's more powerful lower house.
On Friday, Hatoyama dismissed SDP leader Mizuho Fukushima from her cabinet post after she refused to sign off on a U.S.-Japan deal to move a U.S. Marine base on the southern island of Okinawa from a city centre to a less heavily populated area.
He urged her to keep her party in the ruling coalition, but Kyodo news agency said its poll of 47 local SDP chapters on Friday and Saturday showed that 36 wanted to leave.
Asked about the call to stay on, deputy SDP leader Seiji Mataichi said: "It's contrary to common sense and incoherent. Hatoyama has lost normal judgment and is not qualified to be prime minister of a country."
Hatoyama raised hopes during his successful election campaign last year that the Futenma base could be moved out of Okinawa, and abandoning that pledge has angered not only the SDP, but local residents as well.
Coalition and opposition parties called for Hatoyama to resign for failing to keep his promise on Futenma or to meet a self-imposed, end-of-May deadline for finding a solution acceptable to all the parties.
He said on Saturday he would stay on. Some in his own party think he should step down, but time is short for replacing him ahead of the upper house poll, expected on July 11.
Hatoyama's government is seen to have wobbled on a range of promises, from cash allowances for parents of young children to abolishing highway tolls, as it struggles to nurture a fragile economic recovery while reining in ballooning public debt.
"The prime minister said he was putting his job on the line, so naturally, he should resign," said Yoshihisa Inoue, secretary-general of the opposition New Komeito party.
"I think that Futenma symbolises the problem with the nature of the Hatoyama cabinet and politics, that they easily break promises with the people and apologise but take no responsibility."
Media reports said the SDP might continue to cooperate with the Democrats in the election campaign on a local level even after leaving the coalition, but Mataichi said even that would only be possible if Hatoyama resigned, Kyodo said.