The opposition gained ground against Japan's governing coalition in Sunday's parliamentary election, according to preliminary results.
The projected outcome of the election, in which half the seats of the Upper House of Parliament were contested, is viewed as a setback, but not a defeat, for Japan's governing coalition, because it still retains stable control of both sides of the national legislature.
The secretary general of the prime minister's Liberal Democratic Party, Shinzo Abe, plays down the significance of the gains for the opposition Democratic Party.
Mr. Abe says this is merely an interim election, and Prime Minister Junichiro Koizumi should not have to take responsibility for his party performing below the expectations of many inside and out of the party.
Mr. Koizumi told reporters he would not resign, because the governing coalition still holds a comfortable majority in the Upper House.
But he acknowledged voters expressed anger and voted for the Democrats because of unpopular changes to Japan's pension system and public opposition to his dispatch of Japanese soldiers to Iraq.
The prime minister says his party did not have enough time during the 12-day campaign to adequately gain public understanding for its positions on those issues.
The election came as Mr. Koizumi's popularity dropped below 40 percent in recent weeks, the lowest since he took office three years ago.
Opposition Democratic Party candidates cheered that they are now viewed as a viable alternative to the conservatives, who have had a grip on government for nearly all of the post World War II period.
As they celebrated early Monday, the successful opposition politicians vowed to go on the offensive.
Political analysts say Mr. Koizumi's ability to carry out structural reform could indeed be weakened. But they point out it will be the anti-reform old guard within his own party, more than the opposition, that has the real strength to challenge his leadership in coming months.