TEHRAN, Iran — Conservative rivals of Iran’s president claimed control of parliament Sunday with more than two-thirds of the seats decided from elections handing the ruling Islamic establishment near seamless control in the escalating nuclear standoff with the West.

The outcome also puts an emphatic stamp on President Mahmoud Ahmadinejad’s political tumble after he dared to challenge Supreme Leader Ayatollah Ali Khamenei over his power to direct key government affairs such as foreign policy and intelligence.

Ahmadinejad — once considered a favored son of Iran’s theocracy — is left politically weakened moving into his final 18 months in office and could become the first president to be questioned by a hostile parliament since the 1979 Islamic Revolution.

Although the 290-seat parliament holds little control over policy matters such as Iran’s nuclear program, the win by hard-liners looked to reinforce Iran’s stiff rejection of Western pressure to stop its uranium enrichment program.

The West believes Iran is trying to build nuclear weapons. Iran denies that and says its nuclear program is for peaceful purposes.

Speaking in Washington Sunday, President Barack Obama warned that the U.S. would not hesitate to use military force to prevent Iran from obtaining nuclear weapons, but he called for restraint. “Now is the time to let our increased pressure sink in, and to sustain the broad international coalition that we have built,” he told a pro-Israel lobby.

In Iran, hard-liners were claiming victory in the parliamentary elections, though vote-counting continues.

Out of 216 winners that emerged by Sunday, at least 112 were conservatives who turned against Ahmadinejad after he openly challenged Khamenei’s authority last year. Also elected were six independent candidates opposed to Ahmadinejad.

The remaining seats were split between Ahmadinejad supporters and centrists, some of whom could side with the anti-Ahmadinejad bloc. At least 23 races will have to be decided in runoffs. Reformists were virtually absent from the ballots, highlighting the intense crackdowns since the mass protests after Ahmadinejad’s disputed re-election in 2009.

Ahmadinejad and Khamenei started out as close allies, but rifts developed as the president sought to put his stamp on key government posts traditionally under the direct control of the supreme leader. A major break occurred in April when Ahmadinejad boycotted government meetings for more than a week in a personal protest over Khamenei’s order to reinstate the intelligence minister.

The current parliament — which remains in session until the new chamber is seated in late May — is expected to move ahead with an order to bring Ahmadinejad for public questioning over accusations that include economic mismanagement at a time when Iran is being battered by expanded Western sanctions over its nuclear program, targeting ability to conduct international banking and sell oil . Ahmadinejad also is expected to face grilling over his feud with Khamenei.

The final results are not expected until Tuesday, but the partial count was enough for Ahmadinejad’s opponents to boast of a landslide victory.