Bahrain’s embattled Shi’ite opposition movement won big in the Persian Gulf island state’s parliamentary elections, according to results announced on Sunday.

Bahrain’s embattled Shi’ite opposition movement won big in the Persian Gulf island state’s parliamentary elections, according to results announced on Sunday.

The Shi’ite bloc called Al-Wefaq on Saturday won all 18 seats it had contested, a one-seat gain from 2006 elections, making it again the largest force in Bahrain’s 40-member Council of Representatives. No candidate secured a majority in nine districts, setting the stage for runoffs Saturday. Turnout was 67 percent, with more than 300,000 ballots cast.

“We were having difficulties yesterday because lots of names were dropped [from the voter rolls],” said Khalil Al-Marzooq, a returning Al-Wefaq member of parliament, in an interview Sunday. “However, because of the massive participation, we managed to win.”

The vote in the Sunni-led kingdom — a strategic base for the U.S. Navy’s Fifth Fleet — comes amid heightened tensions between the government and the Shi’ite majority.

On Thursday, 23 Shi’ite opposition members will go on trial for charges of plotting a coup. The men were arrested two months ago following weeks of escalating Shi’ite street riots. Human rights groups allege that hundreds more have been detained, deprived of due process, and in many cases tortured — claims the government vehemently denies. Authorities also shut down dozens of opposition websites, including Al-Wefaq’s.

Mr. Al-Marzooq said the crackdown was regrettable and that in addition to pursuing its priority of housing for low-income Shi’ites, Al-Wefaq would seek democratic reforms.

“We want more authority for the Council of Representatives — this is the main thing — and we are looking in the future to have a peaceful transition of power so that the prime minister is elected directly or indirectly from the people of Bahrain,” he said.

The prime minister and members of the Shura Council, the upper legislative body, are currently appointed by King Hamad ibn Isa Al Khalifa.

The election was the third since the king began his political-reform project nearly a decade ago, paving the way for Bahrain’s first elected parliament since the 1970s. While the reforms resulted in greater enfranchisement of the country’s Shi’ites — and of women, who were granted suffrage — it has led to an intra-Shia debate over whether the system is rigged to the point that participation is futile, with four opposition groups having called for an election boycott.

One common complaint of critics involves gerrymandering, which effectively ensures the majority Shi’ites — 60 percent to 70 percent of the population, estimates say — cannot win a parliamentary majority.

Hadi Al-Mosawi, a newly elected Al-Wefaq member of parliament (MP), stated that his bloc had conceded 22 districts, contesting “the only 18 which allow us to be competitive — the Shi’ite areas.” He said there were wide differences in the number of people across districts — differences that tended to favor Sunnis. “One MP can represent 16,000, and another can represent only 1,000,” he said, calling the discrepancy a violation of the “one-man, one-vote” principle.

Mr. Al-Marzooq said that despite the difficulties, Bahraini Shi’ites stood more to gain by working within the system, appearing to regret Al-Wefaq’s boycott of the 2002 elections.

“At least if you have a goalkeeper — even if he is standing against a very good opponent — at least he will defend the goal from lots of balls coming in,” he said.

“This is the situation in Bahrain. If you aren’t in the parliament, then there will be lots of [bad] laws — like what happened in 2002 without the presence of the opposition. The terrorism law, the political-societies law, the gathering law — all of the bad laws — have come from the [2002-2006] parliament, where the opposition was not there.”

“The massive participation,” Mr. Al-Marzooq said, “shows that the boycott debate is over.”