A man in Tehran holds a newspaper with pictures of Iranian President Hassan Rouhani and former president Akbar Hashemi Rafsanjani under a headline that reads "Decisive victory for the reformists." (Photo by Abedin Taherkenareh/EPA)

Early results from this week's pivotal election in Iran indicate that President Hassan Rouhani and his reformist allies have made significant gains, an outcome that could speed up the country's emergence from isolation.

The elections, which will fill the 290 seats in parliament and 88 seats in the Assembly of Experts, were the first since Iran reached a nuclear deal with six major powers last year. With 90 percent of the votes counted as of Sunday, the early results gave Rouhani and former president Akbar Hashemi Rafsanjani the most votes for the assembly. The final results will be announced in the coming days.

"The competition is over — it's time to open a new chapter in Iran's economic development based on domestic abilities and international opportunities," Rouhani said Saturday according to IRNA news agency, adding that the election has given reformists in the government more credibility and clout.

A reformist-backed list of candidates aligned with Rouhani was on course to win all 30 parliamentary seats in Tehran. Top conservative candidate Gholamali Haddad Adel was also set to lose his seat, preliminary results showed.

"The people showed their power once again and gave more credibility and strength to their elected government," Rouhani said, adding he would work with anyone who won election to build a future for the country of 80 million, where nearly 60 percent of the population is under 30.

Iran's interior minister said Saturday that voter turnout was higher than 60 percent, with tens of millions turning out to cast ballots.

In the first substantive comment from the hardline camp, the Revolutionary Guards Corps, a powerful paramilitary organization close to Supreme Leader Ayatollah Ali Khamenei, said the large turnout showed support for the ruling system.

While the Guards' statement praised the contest and implicitly accepted the results, the organization set out the kind of anti-US stance it would like to see.

"The election winners will do their best to protect Iran's dignity, power and independence; resolve the main issues for society and the people; and defeat the global arrogance by their awareness and wisdom," it said, referring to the United States.

The vote for the Assembly of Experts is particularly important, since the body selects the country's highest authority, the supreme leader. Supporters of Rouhani, who promoted the nuclear deal, were pitted against hardliners close to Khamenei, who are wary of detente with Western countries.

Because of Khamenei's health and age, 76, the new assembly members who serve eight-year terms are likely to choose his successor. The next leader could well be among those elected this week.