Conservative rivals of President Mahmoud Ahmadinejad appear on course to gain firm control of the Iranian parliament, according to early election results.

In a huge embarrassment to the president, his younger sister Parvin Ahmadinejad was defeated by a conservative rival in their hometown of Garmsar.

Of 197 winners declared by midday Saturday, at least 102 were conservatives who turned against Ahmadinejad after he openly challenged the supreme leader, Ayatollah Ali Khamenei.

Among the prominent anti-Ahmadinejad victors were Gholam Ali Haddad Adel, whose daughter is married to Khamenei's son, and parliament speaker Ali Larijani, Iran's former nuclear negotiator.

Six independent candidates opposed to the president have also been elected so far.

The remaining seats were split between Ahmadinejad supporters and centrists. At least 15 races will have to be decided in runoffs.

The results indicate Ahmadinejad may face a more hostile parliament in his final 18 months in office and give the ruling clerics a clear path to ensure his successor is a Khamenei loyalist.

The conservatives' lead was expected as the elections boiled down to a contest between conservatives supporting and opposing Ahmadinejad.

Reformists were virtually absent from the ballot, showing the crushing force of crackdowns on the opposition. Instead, Friday's elections became a referendum on Ahmadinejad's political stature after he tried to challenge the near-total authority of Khamenei to decide critical government policies such as intelligence and foreign affairs.

The apparent setbacks for Ahmadinejad's backers, according to early results, could signal a decisive blow in the internal political conflicts and give hard-liners an even stronger say over Iran's nuclear programme.

"It appears that the era of 'Ahmadinejadism' in Iran's political history is gradually coming to an end," said Davoud Hermidas Bavand, a Tehran-based political analyst.

Khamenei said on Friday that Iran was moving into a "sensitive period" in the confrontation over Tehran's nuclear programme, which Iran claims is peaceful but the US and its allies fear could lead to atomic weapons.

The US president, Barack Obama, is scheduled to hold talks on Monday at the White House with Israeli prime minister Binyamin Netanyahu, who is seeking US backing for a possible military action against Iran, but has signalled that Israel is ready to go alone.

In advance of the meeting, Obama stepped up his warnings that it was "unacceptable" for Iran to become a nuclear-armed state.

Yet even before all the final election result, which is expected at the earliest on Sunday, some Iranian officials were calling for a tougher response to the growing international pressure on the Islamic regime.

"Under the present cold war we are in, this election will increase our national security. It will make the US and the west change its tone toward us," said Muhammad Reza Bahanor, a hardliner seeking re-election.

He predicted that 80% of the new parliament will belong to a group known as the ultraconservative Motahed, or United Front, which is the main anti-Ahmadinejad group.

Iran's opposition, crushed in recent years and banned from running in the elections, largely called for a countrywide boycott of the vote. The opposition leaders Mir Hossein Mousavi and Mehdi Karroubi were placed under house arrest in February 2011.

Despite the boycott, reports from Iran suggested many people, especially those in small and conservative cities, participated in the vote.

More than 48m Iranians are eligible to vote in the Majlis elections.