(Reuters) - Defeated hardline candidate Ebrahim Raisi has complained of voter fraud in Iran’s presidential election and called on the judiciary and the election watchdog to investigate, the semi-official Fars news agency said on Monday.

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The allegations, likely to stoke up Raisi’s conservative supporters, were among his strongest since losing the bitterly contested May 19 vote to incumbent Hassan Rouhani by a margin of 57 percent to 38.

Indignant at Rouhani’s re-election, hardliners have vowed to press their conservative agenda. The head of the judiciary on Monday separately criticised Rouhani’s campaign promises to work for the release of two opposition leaders under house arrest.

“Tampering with the numbers of people’s participation is inappropriate. Not sending ballots to centers where the government’s opponent has a chance of getting votes is very inappropriate,” Raisi was quoted as saying.

“I ask the Guardian Council and the judiciary not to let the people’s rights get trampled. If this vote-tampering is not looked into, then the people’s trust will be damaged.”

The Guardian Council is a government body that vets candidates and supervises elections in Iran. It has already approved the results.

But Raisi’s comments were a signal that he and his supporters will continue to put up a fight against Rouhani, who won on promises to increase social freedom, improve human rights and open up the Islamic Republic to Western investment.

His pledges included freeing former presidential challengers Mirhossein Mousavi and Mehdi Karroubi, along with Mousavi’s wife, who have been under house arrest since 2011 after calling for protests in solidarity with pro-democracy uprisings across the Middle East.

“Who are you to break the house arrests?” Larijani said, according to Mizan, the judiciary’s news site.

Larijani said it was for Iran’s Supreme National Security Council to take an initial decision on the detention of the opposition leaders, after which the judiciary would take over.

During the campaign, Rouhani and Raisi exchanged barbs in debates and speeches using language rarely heard in politics in Iran. Rouhani accused Raisi of abuses while at the judiciary, and was in turn accused of corruption and economic mismanagement. Each denied the other’s accusations.

Raisi, a cleric who served on the judiciary for many years, made his allegations of voter fraud to a gathering of supporters on Sunday night, Fars said. He was also quoted as saying Rouhani had inappropriately used TV, newspapers and government offices for campaign purposes.