Japan's ruling coalition clinched a majority in the upper house of Parliament in elections Sunday, but gains by the opposition signaled discontent with the prime minister's cuts in pension benefits and deployment of troops to Iraq.

Japan's major TV networks, citing voting samples, reported late Sunday that Prime Minister Junichiro Koizumi's (search) Liberal Democratic Party and coalition partner Komeito party won at least 58 of the seats under contention, ensuring their dominance of the upper house.

But the opposition Democratic Party boosted its standing in the chamber by at least 11 seats, taking at least 49, preliminary results showed.

Official results were expected Monday morning.

The embattled premier, who took office in April 2001 promising far-reaching reform, insisted there was no reason for him to resign to take responsibility for the results. But the Democrats claimed victory.

"The people have issued a resounding 'no' to Koizumi's policies," said party leader Katsuya Okada.

The election had not been expected to seriously threaten the LDP's hold on government. The party, which has governed almost uninterruptedly since 1955, holds a firm majority in the powerful lower house, the stronger of the legislature's two chambers.

But the robust turnout for the opposition could undermine support for Koizumi within his own party.

"What we're seeing is a result of Koizumi's diminishing popularity -- the 'Koizumi effect' is wearing off," said Jiro Yamaguchi, a political scientist at Hokkaido University. He predicted the party would become even more resistant to reform.

The election also bolstered the emergence of a two-party political system in Japan, with the LDP increasingly balanced by the Democrats rather than easily dominating an opposition splintered into smaller groupings.

Half of the chamber's 242 seats were contested. Before the vote, the Liberal Democrats held 115 seats in the upper house and controlled a majority of seats together with Komeito's 23 seats. The Democrats had 70.

The LDP had set a total of 51 seats -- a gain of one seat -- as its modest goal for the election. While local media speculated Koizumi could face pressure to step down if the goal was not met, the premier dismissed talk of resignation.

"There would be no need for that," he said in an interview with NTV, a nationwide television network. "As long as we can keep control of both houses, we will continue with our reform policies."

LDP coalition partner Komeito -- a party backed by the Buddhist organization Soka Gakkai (search) -- was expected to hold on to the 10 seats it was defending, and perhaps add one or two, the national broadcaster NHK said.

Though one of Japan's most popular postwar leaders, Koizumi's support has been plunging. A survey by Japan's largest newspaper, the Yomiuri, showed Koizumi's support has fallen to 35.7 percent -- the first time it had dropped below 40 percent since he took office in April 2001.

Pollsters attribute the decline to anger over a new law that hikes mandatory pension premiums and cuts benefits -- a major issue in a nation that has the world's longest life expectancy for both men and women and is graying rapidly.

The safety of Japan's troops in Iraq has also been an issue, especially since no Japanese soldier has killed or been killed in battle since World War II.

Responding to President Bush's (search) call for "boots on the ground," Koizumi championed the deployment of several hundred soldiers on a non-combat, humanitarian mission to the southern Iraqi city of Samawah almost six months ago. It was the country's biggest overseas military operation since World War II.

As violence continues in Iraq, many Japanese fear the soldiers could become targets.

The Democrats, emboldened by big strides in the November lower house elections, have appealed to voters to give them a chance to provide a viable, centrist alternative to the LDP.